Appliance Repair Study Unit 4 Electric HeatingAppliances and Fans By Jack Darr Revised By Robert L. Cecci
iii PreviewNow that you have completed the study of the fundamentals of appliance repair, we can beginstudying how to repair heating appliances and fans.In this study unit, you will see how to test and replace components properly. You will see howto disassemble, test, replace and perform a safety test on various heating appliances and fans.In this text, you will begin to see how to troubleshoot actual appliances. You will begin by check-ing power cords. Power cords take the greatest abuse and are the most likely cause of both inter-mittent and total failure in appliance performance. Here, you will also see how to choose thecorrect appliance power cord for each type of appliance.Next, you will see how to repair electric room heaters. We have already used heaters in pre-vious texts for examples of the use of test equipment. Now, you will see how to disassemble,test, and replace heater components. Also, you will see how a heater can be constructed to havemultiple heat ranges.The next heating appliance to be covered will be the electric clothes-pressing iron. This text shallcover the disassembly, testing, and repair of dry, steam, spray, and steam/spray irons.The final two sections of this text will cover room fans, and attic fans/power ventilators. Youwill see how to rebuild a fan unit and how to eliminate electrical problems and problems ofnoise and vibration.At the end of this unit, you will be able to • Describe the features of typical appliance line cords • Identify the proper type and AWG size of appliance line cords • Discuss the purpose and application of devices such as strain reliefs, solderless connectors, and crimp-on lugs • Describe how typical room heaters are constructed • List the steps to proper electric room heater servicing • Describe how electric irons are constructed and how to repair dry, steam, and spray irons • Identify various types of electric fans and list the steps to proper fan repair • Determine how to troubleshoot and repair attic fans and power ventilators
vContentsWORKING WITH LINE CORDS AND PLUGS . . . . . . . . . . . . . . . . . 1 Appliance Line Cords Wire Sizes in Line Cords Zip Cord Jacketed Cord Cords Used in Heating Appliances Selecting Line Cords Line Cords with Grounds Polarized Receptacles Cord Connections Line Plugs and Replacement Stocking Replacement Line Cords Strain Relief Splicing Cords Using Solderless Connections Crimp-On LugsELECTRIC ROOM HEATERS . . . . . . . . . . . . . . . . . . . . . . . . . . 15 How a Heater Works How a Heater Is Built Hints for Servicing Room Heaters Heating Elements Mounting Heating Elements Electrical Connections to Heating Elements Thermostats in Heaters Testing Heaters How to Test a Heater for an Open Circuit How to Replace Heater Parts Testing after Repairs Are Finished Reassembling the HeaterCOMBINATION OF HEATING ELEMENTS . . . . . . . . . . . . . . . . . . 27 Current in Heating Elements Resistance of Heating Elements Multiple-Heat Circuits with Parallel Elements Series-Connected ElementsELECTRIC IRONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Operating Features of an Electric Iron How an Electric Iron Is Constructed How a Dry Iron Is Built
vi Contents Thermostats in Irons Steam Irons Spray Irons Check Valves HOW TO TEST AND REPAIR ELECTRIC IRONS . . . . . . . . . . . . . . . . 41 Testing the Line Cord How to Repair the Line Cord How to Take a Steam Iron Apart How to Take Dry Irons Apart Continuity Test of Heating Element and Thermostat How to Remove Bolts and Nuts from an Electric Iron How to Detect Scale in Steam Irons How to Clean Steam Irons Disassembling Newer Irons Troubleshooting Modern Irons ELECTRIC FANS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Types of Fans How Fans Are Built Fan Blades Two- and Three-Speed Fans How to Take a Fan Apart How to Test the Speed Control Burned-Out Motor Coils Dragging Bearings Worn Bearings Causes of Noisy Fan Operation How to Tighten a Loose Hub How to Check Blade Angles Adjusting Blade Tips Loose Parts on Guards Oscillating Fans Repairing Combination Light/Fan/Heaters Air Purifiers Servicing Air Purifiers ATTIC FANS AND POWER VENTILATORS . . . . . . . . . . . . . . . . . . . 73 Types of Fans and Ventilators Servicing Attic Fans and Power Ventilators CHECK IT OUT! ANSWERS . . . . . . . . . . . . . . . . . . . . . . . . . . 81 EXAMINATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
1 Electric Heating Appliances and Fans plastic insulation. Appliances which draw aWORKING WITH LINE heavy current, such as electric irons and heaters,CORDS AND PLUGS must use a special line cord with heavy wires and high-temperature insulation.Appliance Line Cords Wire Sizes in Line CordsThe wire which connects an appliance to awall outlet is termed the line cord by most The size of a wire determines the amount ofappliance technicians. The line cord is a very current it can safely carry, just as the size ofimportant part. Unless power can get to the a water pipe determines the amount of waterappliance, the appliance will not work. The which can flow through it. The thicker theline cord is also the part which gets the wire, the greater the current it can carry.hardest service; it is bent, kinked, crushed, The wire in a line cord should be largeand even cut. enough to carry the normal current withoutThe line cord is the first thing you should heating up; the heat should be in the appli-check whenever you test a faulty appliance. ance, not in the line cord. If the line cordLook for places where the cord may have should heat from an overload of current,been crushed or even cut. Take the cord and the insulation would go bad in a very shortbend it sharply between your fingers, watch- time, presenting a serious shock hazard.ing the insulation. If the cord is too old, you’ll The size of a wire is indicated by its gagesee fine cracks in the rubber or plastic insula- number. Wire size is generally specified bytion at the bend. Such a cord should be re- the American wire gage (AWG), which is alsoplaced because the insulation will soon fail. known as the Brown & Sharpe gage (B&S).If the cord isn’t in first-class condition, it An assigned AWG number indicates a certaincould be a very serious shock hazard to the wire size, and the amount of current a wireuser. Since practically all household appli- can carry is termed its ampacity.ances are accessible to children, you must Table 1 on page 2 shows the standard wiremake sure that the line cord is absolutely safe. sizes used in all appliance cords and theThe cord insulation must be perfect, not safe current-carrying capacity, or ampacity,aged or broken. All electrical connections of each wire size. Strangely enough, the big-must be tight and well insulated. ger the wire number, the smaller the wire.Bad line cords are the most common trouble For example, AWG No. 12 is much biggersource in all portable appliances. A great than AWG No. 18, and it carries more current.deal of your work will consist of replacing The standard types of cords, according tocords. You must know exactly what kind of insulation, are indicated by letters.replacement cord to use on each appliance. The wire used in the line cord must be ableThere are several types of cords available, to carry the normal current drawn by theand the cord used depends on the appli- appliance, plus a little more as a safetyance. Small, low-current appliances use margin to keep the cord from heating up.cords with small wires and with rubber or
2 Electric Heating Appliances and FansYou learned earlier how to determine the Zip Cordamount of current an appliance will draw.From the nameplate, take the voltage and Small appliances, up to 100 to 200 watts, usethe wattage, and then divide the watts by a lightduty rubber-insulated cord, type SV,the volts to find the current. For instance, if type SPT. Most technicians call this cord aan appliance draws 1200 watts at 120 volts, zip cord. Its wires are parallel, and there isit will use a groove between them. This makes it easy to pull, or zip, the wires apart to makeI = P/E = 1200/120 = 10 amps connections; hence the name “zip cord.” Most small appliances use zip cords with wires from No. 18 to No. 14. Table 1 Size S, SJ HPN Jacketed Cord AWG SV, SPT HSJO Heavier appliances that draw high currents, 18 10 10 such as irons and heaters, need heavier wire 16 13 15 and better insulation. They may need a type of cord designated SV or SJ. If the two insu- 14 18 20 lated wires in the cord have a plastic outer 12 25 25 cover for extra protection, the cord is called a jacketed cord. The two wires are made so 10 30 30 that they spiral around each other, and strands of a special paper or fiber are added between them for extra protection. A jacketedLooking at Table 1, you can see AWG No. 18 cord is used on washing machines, vacuumwire is rated at only 10 amp if it is of the rubber cleaners, and similar appliances which aretype SJ and has two conductors. This wire is used in damp places. The extra protection istoo small. For safety’s sake, use at least an needed where the cord must be able to standAWG No. 14 wire rated at 18 amp, or better hard wear, such as being walked on, rolledstill, an AWG No. 12 wire rated at 25 amp. If up, bent, and flexed. Jacketed SV and SJ cordsyou can’t get the size wire you want, always are made in sizes No. 18 and No. 16. Heavieruse a wire of the next larger size or next smaller jacketed cords, such as Type S with wires upAWG number, and you can’t go wrong. to No. 10, are available for extra-hard use inBesides the greater ampacity it provides, there damp places.is another advantage to selecting a line cordwith wires somewhat larger than necessary.The flexible line cords are all stranded. That Cords Used in Heatingis, many strands of much smaller wire make Appliancesup a wire of a larger size, the number of A special type of cord is used on heatingstrands depending on the cross section of appliances where currents are higher and theeach individual strand. The strands will cord may be burned if it should come in contactinevitably break in use some day. However, with the heater. This cord is called the heaterif you use a No. 12 wire where only a No. 14 cord. The wires are insulated with ethyleneis needed, by the time enough strands break propylene rubber or polychloroprene, andto bring the wire down to the cross section strands of fiber glass are sometimes addedthat will carry as much current as a No. 14 between the wires. The older heater cordssize, the cord will have lasted much longer are covered with a heavy woven cloth braid.and been much safer.
Electric Heating Appliances and Fans 3Heater cords are available with wires from order wires large enough for the job. In yourNo. 18 to No. 14, and among the standard repair work, you will seldom need a cordtypes are HPN and HSJO. with wires smaller than AWG No. 14.Selecting Line Cords Line Cords with Grounds When some strands in a stranded wire break,In Figure 1 are shown the three types of line the cross section of the wire in the line cordcords, the heater cord, the zip cord, and the becomes smaller and the cord will get veryjacketed cord. The jacketed cord is shown hot when the appliance is turned on. If allwith three wires; the third wire is used for strands in the cord break completely, an arcgrounding the case for safety. will form across the very small gap between the ends of the strands and generate high heat which can melt the insulation on the wires, cause a short circuit, and even burn the cord completely in two. In older hand-held electrical appliances, such as electric drills, saws, and mixers, the break- down in the cord can cause the hot wire to come in contact with the metal frame or the case of the appliances. This short circuit can give the person using the appliance a dangerous shock. A safety cord, called a grounded line cord, has been developed toFIGURE 1—Three different types of appliancepower cords are shown here. eliminate this danger. Such a cord has the two regular wires needed to complete theStandard flexible cords are designated by circuit, plus a third wire connected to theletters as indicated in Table 1 on the preceding frame of the unit, as shown in Figure 2 onpage. You may select the cords according an electric drill. This “grounding wire” isto place of usage, such as in dry or damp connected to the frame of the drill and toplaces; or according to degree of usage, suchas “extra-hard usage,” “hard usage,” and“not hard usage.” For example, rubber- MOTORcovered cords SV and SJ are available withNo. 18 wires. Both may be used in dampplaces, but the Type SV is for “not hard usage,”that is, it is used for smaller vacuum cleanersand food mixers, while the Type SJ is for ELECTRIC DRILL“hard usage,” as in larger vacuum cleaners.A similar rubber-covered cord, Type S, is for“extra-hard usage”; it resists alkalies, acids, GROUNDING WIREand water, and is available with wires AWGNo. 18 to No. 10. MOTOR WIRESMost of the time you will select cords fromcatalogs which indicate the insulation, the FIGURE 2—When an appliance has a three-wirebest application, the wire sizes, and the prices power cord, the green wire is grounded and willof available cords. But always remember to attach to the case of the appliance.
4 Electric Heating Appliances and Fansthe ground pin at the plug. The plug on the The circuit opens, the appliance is cut offline end of the cord has a round third prong from the source, and the user is protectedto which the grounding wire is connected. from a possible shock.The two regular circuit wires are connectedto the two flat prongs. Such a special grounded Most modern appliances and power toolsplug and a grounded outlet are shown in use plastic cases. Since plastic is an insulator,Figure 3. The round prong prevents this line the shock hazard present with metal-casedplug from being plugged into an outlet which appliances and power tools is eliminated.does not have the ground as a safety feature. Many of these devices will, therefore, use aThe grounded or polarized outlet has a third simple two-wire power cord. If a three-wirehole, or terminal, for the third prong. This cord is used, the ground lead is normallyhole is D-shaped. attached to the case of the motor inside the appliance or power tool.Most older electrical appliances of all kindsare equipped with a grounded line cordand a grounded plug. To accommodate them, Polarized Receptaclesold outlets with two terminals must bereplaced with the newer grounded outlets, Many outlets, or receptacles, in older homeswhich have an additional terminal for the will not have the third terminal for theprong of the grounded plug. If you expect grounding prong of the cord. If you replaceprotection from the grounded line cord, these receptacles, you should buy polarizedyou must connect the third wire to the receptacles which make the use of the ground-ground, that is, from the round terminal ing cord possible. A polarized receptacle isof the outlet to the ground. recognizable by the three terminals, one of which is D-shaped and marked “ground.”The idea behind all this is simple: If theappliance develops a short circuit (if a wire When replacing a two-wire outlet with aaccidentally makes contact with the appliance three-wire, or polarized, outlet, you mustcase), an arc will form between the broken connect the third-wire terminal to a groundingwire and the grounded wire in the cord, the conductor, or the outlet won’t offer anyhigh current will flow back through the protection at all.circuit to which the outlet is connected andblow the fuse or trip the circuit breaker. Standard color-coding of house wiring is black for the hot side and white for the neutral; the third wire may be green or bare, and is grounded. In the three-wire line cords, this same color code will be followed, and the third wire will always be green. However, do not depend on color-coding. The house may have been wired by an amateur electrician ignorant of the proper coding. Test the wiring to be sure. Cord Connections The connections on both sides of the lineFIGURE 3—A three-wire cord and plug are shown cord are very important. They must be clean,here. Notice that the plug uses a polarized outlet tight, and strong at both ends, so that thewith different-sized blade receptacles.
Electric Heating Appliances and Fans 5cord won’t loosen in service and cause a shortcircuit. The stranded wire of the cord can behard to handle unless the right methods areused. Later you will learn how to makeconnections with stranded wires.The appliance is connected to the line cord (a) (b)through screwed, soldered, or crimp-onterminals, or through a receiver plug. Theline side of the cord has a line plug whichis to be connected to the wall outlets. (c)Line Plugs and Replacement (a) First step (b) Second step (c) Incorrect methodYou can buy a prefabricated line cord forsmall appliances up to about the size ofvacuum cleaners. The line plug is molded FIGURE 5—The replacement of a plug is shown here. (Courtesy of McGraw-Hill Book Company, Inc.)onto one end of the cord, and the other endis already prepared, with the wires strippedand fastened to lugs, as shown in Figure 4. up, though, it won’t be long before the wiresSuch cord is used by most appliance techni- pull out. Figure 5 shows the procedure forcians to save time. fastening the wires to one type of plug. Here’s how to do it.In many jobs, however, you will have to puta plug on the end of a new line cord or replace If you have a zip cord, pull the wires aparta plug that has broken connections on the for a distance of about two inches. Strip offoriginal cord. You must know how to install about 2.5 cm (1 in.) of insulation on eacha plug. Correctly installed, a line plug will wire. You’ll see that the fine strands of thelast a long time. If it isn’t correctly hooked wire are twisted inside the insulation. Twist the free ends in the same direction, to eliminate the possibility of a short circuit or shock hazard. Now, feed the ends of the wires through the hole in the end of the plug, up between the prongs. Tie a knot in the two wires as shown in Figure 5(a), leaving about 3.5 cm (1.5 in.) of wire extending beyond the knot. The knot provides strain relief and holds the wire tightly inside the plug, as shown in 5(b), so that if the cord is pulled, there won’t be any strain on the electrical connections. Never fasten the leads without making a knot as shown in 5(c). The steps in tying this knot are shown in Figure 6.FIGURE 4—A replacement line cord is available Next, wrap each wire around one of thewith special lugs attached for easy connection prongs and then around the terminal screw,to an appliance. which should be loosened about two turns.
6 Electric Heating Appliances and Fans plug body. Sooner or later, the wires will break. When the cord is moved one way, the ends of the break are pushed together and the plug works; when the cord is moved the other way, they pull apart and the circuit is open. For a quick check, hold the plug in one hand and move the cord back and forth. If the appliance suddenly starts and stops as the cord is moved, wires are broken. ReplaceFIGURE 6—A zip cord should have a knot tied in it the plug.to provide strain relief. (Courtesy of McGraw-Hill BookCompany, Inc.) Replacement plugs are readily available. Two types of replacement plugs are shown inBe sure to wrap the wire in a clockwise Figure 8. The plug on the lower left is useddirection around the screw, as shown in for thin two wire or zip cord. To install thisFigure 7. If you wrap the wrong way, when type of replacement plug, the halves of theyou tighten the screw, the wire will be plug are separated and the unstripped zipsqueezed out from under the screwhead. But cord is placed inside one half of the plug.if you wrap the right way, the screwhead will Then, the second half is squeezed onto thepull the wire tighter. Be sure that all strands wire until the locking tabs inside the plugof the wire are under the screw, so that you catch. Teeth within the plug pierce the insu-won’t lose any of the wire’s current-carrying lation of the zip cord to make electricalcapacity. Remember that loose strands of contact with the wires inside the zip cord.wire in plugs or in any other electrical con-nection are an invitation to a short circuit.Molded plugs come as original equipmenton many appliance cords. Such plugs areusually made of rubber or plastic, as shownin Figure 8 (item 1). The most commonuser’s complaint about this plug is thatsometimes it works when it is plugged inand sometimes it doesn’t. Here’s what hap-pens. As the cord is pulled back and forth, itbends at the point where it comes out of the FIGURE 8—Two types of replacement plugs are shown here. RIGHT WRONG The replacement plug on the upper right is a heavy-duty three-wire plug. The front and rear of the plug are separated by loosening the screws on the front side of the plug. The wires are then placed on their proper termi- nals and the internal screws are tightened to hold the wires. The front screws are thenFIGURE 7—The correct method of attaching a tightened to hold the plug halves together.wire to a terminal is to wind the wire in a A clamp in the rear of the plug also has twoclockwise-direction, hook the wire around thescrew, and tighten the screw. (Courtesy of McGraw-Hill Book Company, Inc.)
Electric Heating Appliances and Fans 7screws that are tightened to firmly clamp Stocking Replacement Linethe wire at the rear of the plug. CordsSince most bending and flexing takes placeat the plug end and at the point where the When you’re starting in the appliance repairline cord enters the body of the appliance, business, it is a good idea to stock about halfyou’ll find practically all of the accidental a dozen ready-made line cords with plugs.breaks in line cords at one of these points. Later on, you can buy the right kind of cord,In fact, many technicians, when they find in full reels, and a stock of plugs, and assem-an open line cord by testing, simply cut the ble the line cords and plugs as you need them.cord at a point about 15 cm (6 in.) from the This saves a little money. You can also makeplug. They strip the wires and test again. If the replacement cord longer than the originalthey now get continuity in the cord, they line cord if the customer wants it that way.replace the plug and the job is done; if not,they replace the whole cord, since it isobviously open at the other end or some- Strain Reliefwhere in between the ends. An appliance usually has an attachmentMany appliance repair persons are now using which holds the cord in place and relievesa two-piece plastic replacement plug. This strain on the electrical connections. Such anplug uses a compression system to hold the attachment is called the strain relief. Therewires to the plug’s terminals. To use this type are several different kinds of strain-reliefof replacement plug, you strip the outer jacket devices, but they all serve the same purpose.cover back approximately 4 cm (1.5 in.) andstrip 6 mm (.25 in.) off the wires. Place each If the appliance case is metal, the cord needswire into its proper terminal and tighten the some protection to keep the sharp edges ofscrews. The terminal’s screws are normally the hole from cutting the insulation. A smallcolor-coded so that it is easy to install the soft-rubber grommet is pushed into the hole,wires to the proper terminals. The green as shown in Figure 9(a). The cord passesscrew is always used for the green wire through the grommet, and an overhandwhich is grounded. The silver screw is used knot is tied on the inside to keep the cordfor the white wire which is neutral. Finally, from being pulled through again. When youthe copper-colored terminal is used for the are replacing the cord, always leave a littleblack wire which is the AC feed of 120 VAC. slack in the wire between the knot and the electrical connections.To complete the assembly, one of two typesof strain relief will be used on the plug. One In some appliances you’ll find the grommettype uses a tapered barrel and rubber or foam and a small metal clamp which holds the cordinsert. This type of strain relief is installed to the side of the case, as in 9(b). Others willby simply tightening the tapered barrel onto use a plastic strain-relief device, which isthe plug assembly. As the barrel is tightened, folded over the cord and then pushed intothe rubber or foam insert is compressed the hole, as shown in 9(c). The insulationaround the wire. is compressed, then it snaps back, and the device is held in place by notches moldedThe second type of strain relief uses a split in its sides. This device is used mostly withrear barrel which is tightened around the the flat SJ cord or the zip cord, but you canwire by means of two screws. find larger sizes for use with round SV cords and larger cords.
8 Electric Heating Appliances and Fans CASE RUBBER GROMMET KNOT (a) RUBBER GROMMET METAL CLAMP (b) PLASTIC STRAIN RELIEF (c)FIGURE 9—Three types of strain relief are shown here. In (a) and (b), you can see a soft rubber grommetbeing used. In (c), a split grommet is being used.If an appliance does not have any strain pro- Splicing Cordstection, add such protection. If the hole isn’tlarge enough to take a grommet, enlarge the If you find that the line cord of an appliancehole and put a grommet in. The appliance is broken in the middle, examine the cordwill be much safer. very carefully. If the insulation on the whole cord is even slightly cracked, replace the whole cord. Making a splice in a cord is the exception and not the rule.
Electric Heating Appliances and Fans 9There’s an easy way to make a splice. Always on the other. Now, strip the insulation off allremember that the splice must be as strong the wires, for about 2.5 cm (1 in.) or less. Manyas the rest of the cord, and perfectly insulated. professionals strip wires with a wire stripperWith modern tapes and methods, it is possible like the one shown in Figure 10(a).to make small neat splices that will last.Here’s how you do it. Hold the insulation between the stripper jaws as shown in 10(b), without applyingCut the cord at the break. Strip off about 5 cm too much pressure, so as to avoid cutting(2 in.) of the outer jacket, using a sharp knife. the wires. Then give a sharp yank towardNext, hold the two ends of the cord together the end of the wire; the insulation will comeand cut off 2.5 cm (1 in.) of the black wire on off, leaving the wires exposed. This takes aone end and 2.5 cm (1 in.) of the white wire little practice, but it is the fastest way.FIGURE 10—A typical wire stripper and crimper is shown in (a). Figure (b) shows how to strip wire with thistool. (Photos Courtesy of Robriair Manufacturing Company)
10 Electric Heating Appliances and FansIf the wire is clean, start splicing. If it has on a single layer of tape. When you get todarkened with age, it is a sign to replace the other end, cut the tape off and smooththe wire. To splice the wire, place the ends it out. Next, put on the final layer in the otherof the black wires together, and twist the direction. Pull the tape as tight as possible sobare parts over one another. Be sure that all that the splice will be well insulated. If thisstrands are in place. The splice should not cord will be used in a damp place, spray abe thicker than 12 mm (.5 in.) of bare wire. thin coat of acrylic plastic over the wholeSolder the splice smoothly. Be sure that the splice. This will seal the tape very tightlysolder runs well into the wire. If solder is and make your splice as waterproof as theexposed, either melt the solder again or file original cord.the sharp points off before taping. Suchpoints could punch through the tape andcause a shock hazard or short circuit. Using SolderlessAfter soldering, tape the splice. It is easier to Connectionstape one completed splice before you splicethe other wire. Use plastic electrician’s tape Inside many appliances, you’ll find solderlessand wrap the tape neatly over the bare parts connectors like the one shown in Figure 12(a).of the splice, going up over the insulation at These are little bell-shaped devices madeboth ends. Stretch the tape over the splice of insulating material, usually plastic, andalmost as smoothly as the original insulation. often called wire nuts. They are used mostlyTwo layers of tape are enough. on small stranded wires. Large sizes are available for use on solid wires, such as theNext, splice the other wire just as you did types used in house wiring.the first one, pulling the wires apart in a“bow” so that you can reach the wire being You can connect up to four wires with aspliced without melting the tape on the first solderless connector, depending on the sizewire. Tear off a short piece of tape because connector used. To make a connection likeyou’ll have to thread this tape through the this, strip the ends of the wires back aboutloop of the two wires. 6 to 10 mm (.5 to .75 in.) and put them side by side with the bare wire ends parallel, asNow you can see why we cut the two wires shown in 12(b). The ends of the insulationat odd lengths: the two splices are staggered should be exactly the same length.(they are not next to one another) as shown inFigure 11. This staggering lets you put on the Now, put the wire ends inside the open endfinal wrap of tape without leaving a big lump of the wire nut shown in 12(c). Screw the wirein the cord. Start the taping well back up on nut on in a clockwise direction because itthe jacket, about 2.5 cm (1 in.) or so, and wrap has a right-hand thread. The small metalFIGURE 11—The proper method of winding the wires for an inline splice is shown here. Crimp-on inlinesleeve splices may also be used. (Courtesy of McGraw-Hill Book Company, Inc.)
Electric Heating Appliances and Fans 11 THIMBLE SPIRAL SPRING (a) (b) (c)FIGURE 12—A typical wire nut is shown in (a) with the correct method of installing the nut in (b) and (c).(Courtesy of McGraw-Hill Book Company, Inc.)spring inside the wire nut, shown in 12(a), then replace the connector with a wire nut.will catch the wires and pull them up inside The connection will be just as good as thethe insulator. Keep on turning until the original.connection is very tight. Make sure that theinsulation of all wires is covered by the flared Crimp-On Lugsend of the wire nut. If it isn’t, a short circuitmay develop later on. In many appliances, especially those using screw terminals, you’ll find a special kind ofThe solderless connector is especially handy terminal lug called a crimp-on lug, which canbecause it can be taken apart for testing and be attached without soldering.then put back without the use of tools. Insome appliances, you may see connectors The crimp-on lug has a hollow sleeve for thewhich look like wire nuts but aren’t. These wire and a lug which will serve as a terminal.are the crimp-on types which are permanently Strip the wire just enough to go through thisattached by crushing the sleeve inside the sleeve, no more. Push the wire through theinsulator. These can’t be taken apart and put sleeve, making sure that the insulation isback. However, if necessary, you can cut tight against the end of the terminal and thatsuch a connector off, make your tests, and the ends of the wire do not go through too far.
12 Electric Heating Appliances and FansIn factories the crimp-on terminals areinstalled by a machine. In your shop, youcan crimp the sleeve by using the crimp-ontool, which is the top part of the wire strippershown in Figure 13. Pull hard on the crimp-onconnector to make sure that it does have agood grip on the wire.Solderless crimp-on connectors are availablein several different types, such as spade lugs,ring lugs, wire connectors like the wire nuts,and splicing sleeves.When a splicing sleeve is used, the two wireends are pushed into each end of the sleeveuntil they overlap, and then the sleeve iscrimped. An insulator sleeve can be slippedover the finished joint or the joint can betaped. Splicing sleeves can save time if youdon’t want to heat up a soldering iron ordon’t have one with you. FIGURE 13—Crimp-on terminals of many different
Electric Heating Appliances and Fans 13 ✔ Check It Out! 1 At the end of each section in your Appliance Repair text, you will be asked to pause and check your understanding of what you have just read by completing a “Check It Out!” Writing the answers to these questions will help you review what you have studied so far. Please complete Check It Out! 1 now. 1. What is the most common trouble source when a portable appliance does not work? _________________________________________________________________________ 2. Why is defective insulation on a line cord dangerous? _________________________________________________________________________ 3. What is meant by No. 16 AWG wire? _________________________________________________________________________ 4. Define ampacity. _________________________________________________________________________ 5. Which wire carries more current, AWG No. 12 or AWG No. 14? _________________________________________________________________________ 6. What happens if the wire in a line cord is too small? _________________________________________________________________________ 7. What kind of insulation is used on heater cords? _________________________________________________________________________ 8. Why are some line cords equipped with three wires and a three-pronged plug? _________________________________________________________________________ 9. To what should the grounding wire in a line cord be connected? _________________________________________________________________________ 10. How can you recognize polarized, or grounded, outlets? _________________________________________________________________________ (Continued)
14 Electric Heating Appliances and Fans ✔ Check It Out! 1 11. What relieves strain on the wire in a line plug? _________________________________________________________________________ 12. Why are line cords made with stranded wires? _________________________________________________________________________ 13. If you cannot get the original size wire for a line cord, what size should you select? _________________________________________________________________________ 14. When you connect a wire to a screw terminal, how should you wrap the wire around the screw? _________________________________________________________________________ 15. Why is a grommet used in appliances? _________________________________________________________________________ 16. What is the probable cause of trouble if an appliance works at certain times and fails to work at other times? _________________________________________________________________________ 17. How many layers of tape are used for splices? _________________________________________________________________________ 18. What are wire nuts? _________________________________________________________________________ 19. What are crimp-on lugs? _________________________________________________________________________ Check your answers with those on page 81.
Electric Heating Appliances and Fans 15 element rated at 600 watts. This higher-out-ELECTRIC ROOM HEATERS put element would have half the resistance of the 600 watt element.How a Heater Works If the voltage supply is constant, the high current is obtained by low resistance of theOne of the simplest of electrical appliances heating element. The lower the resistance,is the electric room heater. The main part of the higher the current, and the greater thethe heater is the heating element, or heating heat produced by the heater if the voltagecoil, which is made of special resistance wire. remains the same. Electric heaters are ratedWhen voltage is applied to the heater circuit, in wattage, such as 500, 750, or 1000 watts.a current passes through the heating element The higher the heater wattage, the moreand causes it to get hot. The rate of heat heat it produces. A heating element shoulddeveloped in the heating element depends always be replaced with a new one of theon the electric power drawn by the heater. same wattage, so that the unit will produceRemember that electric power, or wattage, the same heat as it did when it was new.is a product of voltage and amperage. Walloutlets supply alternating current at 120 VACto the heating coil. If the current is high, the How a Heater Is Builtpower will be high, and the generated heatwill be high. For example, if a current of 10 Each basic room heater is enclosed in a heavyamps (amperes) flows through the heating metal case. A common heater is shown inelement, the power drawn by the heater is Figure 14. Grilles or screens cover the openings120 × 10 = 1200 watts and the heat will be so that the heated air can circulate to thedouble the heat produced by a 5-amp room. Metal reflectors are used to direct the FIGURE 14—This heater is typical of the many different types of ribbon element heaters.
16 Electric Heating Appliances and Fansheat where it is wanted. Some heaters have with mica sheets or ceramic pads sosmall fans which force out the hot air. The that the heating element can’t touchair then circulates faster around the heater the frame or case.and heats the room quicker. 3. Safety switches, thermostats, and otherHeating elements are mounted on heat-proof safety devices must be checked to makeinsulators to keep them from making electrical sure that the contacts are not weldedcontact with the metal case. In Figure 14, the together or stuck so that they would beheating element is wound diagonally up useless.and down inside the case. The heatingelements are made of special wire which 4. All electrical connections, such as thehas certain resistance and is able to with- connection of the line cord to the heat-stand high temperatures without melting. ing element, must be very clean andAn electric heater may be provided with tight, to avoid developing heat wherea switch that turns the heater on and off. it is not wanted. A hot joint will heatSome heaters have a thermostatic switch in up and oxidize rapidly when carryingaddition to the on-off switch. The thermostatic the heavy current needed in the heatingswitch, or thermostat, turns the heating element, and will burn up.element off automatically when the room 5. When replacing ON/OFF switches, be surereaches the proper temperature. Some other that the new part has the same rating asheaters have safety switches which turn the the original switch. The rating must bepower off if the heater should be tipped over. high enough to do the job. For instance,This is done to prevent any fire hazard. some toggle switches are rated 5 amp at 120 volts, which means a power of 5 × 120 = 600 watts. If you put one ofHints for Servicing Room these on a 1500-watt heater, it will failHeaters in a very short time. Always use parts which have ratings at least 1.5 timesBefore we discuss actual units, there are a the maximum current needed by thefew rules which apply to all resistance wire particular appliance. At 120 volts, theheaters: current through a 1500-watt heater is 1500/120 = 12.5 amp. The rating should 1. The line cord for room heaters rated therefore be at least 1.5 × 12.5 = 18.75 above 500 watts should be high- amp. Use a standard switch rated 20 temperature heater cord. For safety, the amp at 120 volts. You know that this wire in this cord must be large enough switch will work safely and last a long to carry at least 1.5 times the normal time. current. Insulation on line cords must always be in perfect condition, to avoid shock hazard to users. Heating Elements 2. Heating-element support insulators Electric heating elements are usually made must be replaced if they are cracked. If of a special nickel-chromium alloy wire the heater uses open wire as a heating called Nichrome, or from a tungsten-based element, the wire must be tight, so that material. These metals have a very high it can’t sag and touch the metal frame melting point, which is necessary because or case. Enclosed heating elements, the metal gets red hot when in use. Copper like those used in electric irons or wire oxidizes very quickly if red hot and coffeepots, must be very well insulated will burn up in a short time. Nichrome wire
Electric Heating Appliances and Fans 17and other special alloys will stand manyheatings and coolings without too muchoxidation. This wire has a higher resistancethan copper and other metals, and it there-fore, takes a shorter length of Nichrome ortungsten wire to make up a heating element.In the electrical business, heater wire is oftencalled resistance wire.A heating element can be made of round wirecoiled like a spring, or of flat ribbons of varioussizes. Some elements are made of bare wiresmounted on insulators. Others are sealedelements which use resistance wire insulatedwith a ceramic material and placed insidea metal tube which looks like a pipe. Sealedelements must be used in any applicationwhere the surface of the heating elementmust be grounded, as in electric ranges andwater heaters. FIGURE 15—A ceramic heater uses a specialResistance wire has two special characteristics ceramic heating element and many safetythat you must remember. First, since it gets devices. (Courtesy of Rival Manufacturing Company)red hot while heated, you can’t use any rubberor plastic insulation on it. The element willnot only be hot in the physical sense, but push it out, and replace it with a bolt andelectrically “hot” as well. All insulators used nut, and connector.must be able to withstand the high heat and One type of modern electric room heater isat the same time give enough electrical insu- the ceramic heater. A typical ceramic heater islating protection. As mentioned, open-wire shown in Figure 15. The ceramic heater hasand sealed elements in heaters use insulators a resistance element encapsulated in a ce-of ceramic material. Elements in electric ramic material. A fan is used to move airirons and coffeepots use flat sheets of mica through the ceramic heating element. Thisor preformed ceramics. type of heater also normally has manySecond, you can’t solder resistance wire. safety devices such as overload switchesOne reason is that the heating element heats and tip-over switches, along with switchesto a temperature higher than the melting to select fan only, or fan with heat and an ad-temperature of solder. Another is that solder justable thermostat.will not stick to the wire, because of its com-position. Therefore, all electrical connectionsmust be made tight mechanically; that is, with Mounting Heating Elementsbolts, nuts and special connectors. A typical coiled heating element mountedIn some of the cheaper appliances you’ll on ceramic insulators in a small space heaterfind the electrical connections are made by is shown in Figure 16. The coil is tight be-riveting together the ends of the heater wire tween the insulators; this is a key point toand the line cord. To replace this kind of remember.connection, file off one side of the rivet,
18 Electric Heating Appliances and Fans insulating shoulder washer which fills up the hole in the metal frame so that the bolt can never make electrical contact with it. The most important part of this connection is the insulation between the bolt and the frame. The shoulder on the insulating washer must be in good shape, so that it will fill the hole with insulation. Sometimes you’ll find that this shoulder has been crushed by care- less installation, or broken off. If so, put on a new one. Mica washers are often used, but they are very brittle and must be handled with care. They will stand high pressure as long as it is applied properly, but you can break them when they’re loose. When preparing a joint, put the shoulderFIGURE 16—Since the coiled wire heating element washer in the hole first. Then slip the flatcarries 120 VAC, the element must be supportedby insulators such as the ceramic insulators metal washer and flat insulating washershown here. over the bolt, and put the bolt through the hole. Put the other flat metal washer overAn exploded view of a complete room the bolt, and run the first nut down withheater is shown in Figure 17. It has a ribbon- your fingers to hold all of the insulators intype open element wound between bars of place. Tighten the nut with a socket wrench,ceramic material. You’ll find similar heaters holding the bolt with a screwdriver. Don’tusing coiled elements. As long as the total use too much force, or you’ll crush the micawattage and length are the same, there is no washers. Before you continue your work,difference between the ribbon and coil type; test the connection to be absolutely sureone could be used in place of the other. that it is not shorted to the frame. Now put on one of the flat metal washers, wrap the wires clockwise around the bolt,Electrical Connections to and put on the other flat metal washer andHeating Elements the second nut. Be sure that the insulation on the line cord is as close as possible toAll electrical connections to heating elements the connection. Don’t let any of the insula-must be clean and mechanically very tight. tion get between the washers. Tighten the connection down until it is firm, but not tooYou’ll find many connections made with a tight. If the connection is too tight, you’llbolt, using two nuts and flat insulating and crush the wires or make them squeeze outmetal washers, as shown in Figure 18 on between the washers. With only very littlepage 20. The first nut is used to hold the bolt practice, you’ll learn just how much forcetight to the metal frame or bracket, and the to use.second nut is used to make the electricalconnections. The bolt must be completely A connection prepared as just described forinsulated from the metal bracket or the frame a small room heater is shown in Figure 19(a)of the appliance. This is done by using flat on page 21. The heating element is connectedinsulating mica washers between each end to one end of the bolt, and the line-cord wireof the bolt and the metal, and a special is connected to the other end, on the opposite
Electric Heating Appliances and Fans 19 FAN BLADE MOTOR HANDLE RIBBON TAKE-UP REAR COVER CHROME ELEMENT PROBE INSULATOR ASSEMBLY SWITCH GRILLE WRAPAROUND REFLECTOR PAN SWITCH THERMOSTAT BLOCK KNOB INSULATOR SECONDARY ELEMENT CORD THERMOSTATFIGURE 17—Notice the many components used in an electric room heater. (Courtesy of Arvin Industries, Inc.)side of the bracket. Does this make any materials will with successive heating anddifference? Not at all; the bolt makes electrical cooling cycles.contact between them. The most important consideration in usingA close-up view of one of these terminals is the stainless steel terminals is that the crimpshown in Figure 19(b). The mica washers be- is tight on the wire. Special crimping toolstween the first nut and the metal frame are are available for tightly crimping stainlessclearly visible. The second nut and washers steel terminals. Also, many heavy dutyhold the line-cord wire. Many modern resis- crimpers, such as those on a large pair oftance-wire type heaters will use crimp-on electrical lineman’s pliers, can be used.terminals for the power line connections tothe heating element. These terminals areusually made of a stainless steel alloy. Why Thermostats in Heatersstainless steel instead of copper terminals?Stainless steel has many advantages. First, As you progress through this course, you’llstainless steel can be heated and cooled learn that thermostats are used in manythousands of times without the annealing, different appliances. You should know howor softening of the metal. Second, stainless they work. The name “thermostat” meanssteel does not oxidize, or discolor and rust, “constant heat” (thermo = heat and stat =as most other standard crimp-on terminal constant). Thus, a thermostat is a device
20 Electric Heating Appliances and Fans CORD INSULATION SECOND NUT FLAT METAL WASHERS FIRST NUT STRANDS OF BARE WIRES FLAT METAL WASHER INSULATING SHOULDER WASHER METAL BRACKET OR FRAME FLAT INSULATING WASHER FLAT METAL WASHER BOLT BOLT HEADFIGURE 18—The connection to a heating element may be made by means of a bolt and a series of insula-tors and nuts.which is used in heating devices to keep the different rates when heated. Such a blade isheat at a constant level. shown in Figure 20(a) on page 22. The two different metals are indicated by 1 and 2.A thermostat switches off the power supplied One end of the blade is held in a clamp.to the heating element when the temperature When the blade is cool, it is straight. If it isincreases above a certain level, and it turns heated, metal 2 expands much more thanthe power back on when the temperature metal 1. Therefore, the blade bends from thefalls below a certain level. The thermostat “push” of metal 2 against 1, as shown in 20(b).can operate at any given temperature, at avery low temperature in refrigerators and Heat can be applied to the blade in severalat a very high temperature in furnaces, ways. In the simpler thermostats, the currentdepending on the type and setting of the passes through the blade itself. The heatingthermostat itself. effect developed by the blade resistance controls the bending. If the heater drawsEach thermostat has a temperature-sensitive too much current, it becomes too hot. If aelement. This is usually a bimetal blade. A pair of switch contacts are attached to thebimetal blade is a flat metallic strip made free end of the blade, as in 20(c), they willof two different metals which expand at open when the blade bends due to high
Electric Heating Appliances and Fans 21FIGURE 19—The connections to a coiled-wire type heater are shown in (a) and magnified in (b).temperature. This turns the heating element the type of appliance. For instance, a dropoff, and the temperature drops. When the in temperature would close the switch ofblade cools off enough, it straightens, the a heating unit, while a rise in temperatureswitch contacts close, the current starts would close the switch of a cooling orflowing again, and the heater gets hotter. refrigeration unit. Thermostats can be made to work due to a small or a great change inIn more elaborate thermostats, a separate temperature. The exact characteristics of theheating coil is placed under or around the thermostats differ in various types of heaters.blade. The electrical contacts are attached tothe blade but may be insulated from it. Nocurrent passes through the blade; the bladeis heated by the coil. The actual control of Testing Heatersthe electrical circuit is done with relays hav- The testing of electric heaters is very simple.ing heavy-duty contacts, since heavy cur- Turn the heater on and see if it gets hot. If itrents must be switched on and off. In this doesn’t, you should test to find out why it isway, the thermostat blade can be made not working. If there is a short circuit, it willmuch more sensitive to small changes in blow the fuse or trip the circuit breaker. Thistemperature. is one of the easiest faults to locate becauseYou’ll find thermostats in all shapes and it has very obvious symptoms. If the heatersizes. Some will have coiled-spring blades doesn’t get hot when plugged in and turnedinstead of flat blades. However, they all on, then there is an open circuit somewherework in the same way. A rise or fall in tem- in the heater circuit.perature causes the blade to move, opening Before going any further with testing theor closing an electrical contact and acting as heater itself, make sure that the heater isa switch. The particular action depends on supplied with the proper voltage. This test
22 Electric Heating Appliances and Fans CLAMP 1 2 (a) CLAMP 1 2 (b) CURRENT CLAMP ELECTRICAL CONTACTS 1 2 (c)FIGURE 20—Because of the use of dissimilar metals, the thermostat will move when heated. Notice thedifference between the cool blades (a) and heated blades (b). Figure 20(c) shows a set of contactsconnected to the blades.should be made first when testing any elec- should be replaced if it does not hold thetrical appliance. It can save time. No appli- plug prongs tightly.ance can work if it does not receive voltagefrom the wall outlet or from another source.The fastest way to check the wall outlet is to How to Test a Heater for anmeasure the voltage. If the voltage measures Open Circuitaround 120 VAC, then you know that thevoltage is available and that the circuit fuse After making sure that a normal voltageis not blown nor the breaker tripped. supply is available at the wall outlet, you’ll have to take the appliance apart to get at theWhen you plug in an appliance, note how electrical connections. For safety, thesethe line plug fits into the outlet. It should connections are always on the inside of thenot slip in too easily. You should always feel appliance. First, be sure that the line plugsome friction as the prongs of the plug slide is pulled out of the wall outlet and lyingbetween the spring contacts inside the outlet. where you can see it. Now, you can workThis friction is absolutely necessary for a and test in safety.good connection. Old and worn outletsaccount for many electrical troubles when Most small heaters are housed in metal casestheir contacts become loose. The outlet with grilles for better air circulation. The grilles are held in place with small screws
Electric Heating Appliances and Fans 23at the corners or edges. You’ll be able to see across the switch should be cause for switchthrough the grille to test the connections. replacement. The reason for the replacementWhen you remove the grille or any cover, of the switch is that heat caused by the resis-put the screws, knobs, and all small parts tance within the switch will cause the switchyou take off into a little box, so that they’ll to fail in a short period of time.all be readily available when you are readyto put the heater back together. This simple The final test to make is across the heatingmeasure can save a lot of time, and time is element. Typical resistance-wire type heatersmoney. are in the range of about 4 to 20 ohms depending upon the wattage of the heatingIf the heater has three parts, the line cord, element.the switch, and the heating element, youhave three possible sources of trouble. We have described these tests in detail soAlways remember the following rule, which that you can get used to the procedure ofapplies in every case of electrical trouble: testing. Actually, in any of the open-wireThere are as many possible causes of heating elements, you won’t need any testtrouble as there are parts in the circuit. equipment to find an open element, except your eyes. A break in the element will beTests of the three parts are shown in Figure 21. easy to see. However, if the element isn’tThe safest tests are continuity or resistance visible, or if it is one of the sealed types, youtests which can be made with the power must use electrical tests to locate the trouble.removed from the heater.The first two tests to make are continuity testsof the line cord as shown at positions 1 and How to Replace Heater2. The line cord should show near zero resis- Partstance from each of the prongs on the plugto the terminal of the switch and the neutral After you have located the faulty part, replaceside of the heater element. it with a new one. Do not try to repair it. When making replacements on any kindThe switch should be tested next. With of appliance, it’s always best to use exactthe switch in the OFF position, you should duplicates of parts if you can get them. There’sread infinity ohms across it. With the switch a simple reason for this: The duplicate partturned to the ON position, you should read will mount exactly like the old one, withoutnear zero ohms. Any reading above one ohm trouble. Switches, for instance, are often mounted by two ears or brackets held by small screws or bolts and nuts. If the new switch were a little larger than the old one, 3 you’d have to drill a new mounting hole in SWITCH the case. This would leave the original hole exposed and make a sloppy-looking job. 1 HEATING Replacement line cords must be heavy enough 4 ELEMENT to carry the heater current. Replacement 2 switches must have a current rating at least LINE CORD as high as the original or they’ll burn up in a little while. Heating elements should always have the same wattage as the original.FIGURE 21—These are the points at which youcan make resistance or continuity tests on theheaters.
24 Electric Heating Appliances and FansWhen you are going to replace a coiled or a Check the whole heater again very carefully.ribbon heating element, leave the old one in All connections should be tight and the ele-place until you have obtained the new one ments properly mounted. Be critical of yourand are ready to do the job. By doing this, own work. It is much better for you to findyou can see exactly how the original element a small mistake than to have the customeris mounted and how it is wound around the find it. The skilled professional technicianinsulators and racks. If you should have to is never certain that an appliance will worktake the old one out, make a rough sketch until he turns it on and sees it work.of how it was mounted on the insulators.This will save you time if several days elapse The most important test is the safety check.between the time you take it out and the time This test makes sure that there are no shortyou put in the replacement. circuits, or grounds, between the electrical parts and the case. These could cause a veryTo replace a coiled element, be sure that it dangerous shock hazard to the users. Theisn’t stretched too much while putting it in first test for ground should be made withplace. If it is, it will be loose on the insulators a meter set for high resistance, between theand could fall off and cause a short to the line-cord prongs and the case, with the switchcase. First fasten one end to the terminal, then turned on. This should read an open circuitvery carefully thread it around the insulators on a digital VOM, or no deflection at all onuntil you get to the other terminal. Ordinarily the ohm scale of an analog VOM. Reviewit will be a little short because the coil hasn’t the rules given in previous lessons for howbeen stretched. Stretch it very gently until to make continuity tests and leakage teststhe open end just reaches the other line with various test equipment.terminal. You may have to stretch it slightlyin the middle to get enough slack. Try to You should never hesitate to make duplicatedistribute the tension over the whole element; tests or to make the same test in severalit will last longer. different ways. For another test for grounds, connect one lead from the meter set to ACWhen replacing the flat-wire, or ribbon, volts to a good ground, such as a water pipe.elements, each turn of the element should Now, plug the appliance in and turn it on.fall into a notch or hook on the mounting Touch a bare metal part of the case with theinsulators. Check the path and location of other lead from the meter, as shown Figure 22.the original element very carefully before If you measure no voltage, the applianceyou take it off. Don’t let the ribbon elements is safe.twist; this puts an excessive strain on themwhen heated and can cause early failure.Later on, you will study about other typesof heating elements such as those used on HEATER DIGITAL VOMwater heaters and electric ranges. We’lldescribe in detail the mounting of each typeof element as we come to it. OUTLETTesting after Repairs Are WATER LINE CORD BARE PIPEFinished METAL PARTNow we come to a very important part ofthe job: testing to be absolutely sure that FIGURE 22—This diagram shows how to perform athe appliance will work just as it did when leakage test on the case of a heater or otherit was new, and that it will be safe to use. metal-cased appliance.
Electric Heating Appliances and Fans 25Reassembling the Heater If you can’t find an exact duplicate screw and the missing screw is visible from theAfter all the tests have been completed, front, look underneath or on the back. Takeput the heater back together. Be sure that out an original screw from there, replaceall screws are replaced. That’s why you it with another type, and put the originalput them all in the same box, to keep them screw where it can be seen. This makes thetogether. Quite often, appliances will come job look neat. Careful attention to little detailswith screws missing. Replace the missing like this will help you build up a reputationscrews with new ones from your stock. The as a really skilled craftsman. Don’t ever over-appliance will then be returned to the owner look details.as good as new. Match the original screwsas closely as possible. In most cases, thiswon’t be hard to do.
26 Electric Heating Appliances and Fans ✔ Check It Out! 2 1. How does a thermostat control heat? _________________________________________________________________________ 2. Why does a thermostat use a bimetal blade? _________________________________________________________________________ 3. What is the probable trouble if the heater does not heat up when plugged into an outlet with the switch closed? _________________________________________________________________________ 4. If a heater is designed to carry a normal current of 10 amp, what should be the minimum current-carrying capacity (ampacity) of the line cord? _________________________________________________________________________ 5. What kinds of insulators are used for mounting heating elements? _________________________________________________________________________ 6. How should the connections of a heating element be made? _________________________________________________________________________ 7. Why should you slightly stretch the heating coil when mounting it? _________________________________________________________________________ 8. What check should you make after the heater has been repaired? _________________________________________________________________________ 9. How is the check for grounds made? _________________________________________________________________________ Check your answers with those on pages 81–82.
Electric Heating Appliances and Fans 27COMBINATION OF Resistance of HeatingHEATING ELEMENTS Elements When you know the current drawn by the heating element from an AC line, you canCurrent in Heating Elements determine the resistance by the formula of Ohm’s law:The amount of heat produced in a device ismeasured in calories or British thermal units R = E/I(Btu), but we seldom need to know howmany calories are produced by a toaster, an in whichelectric range, or any other electric heating R = resistance, in ohmsappliance. We are mainly interested in findingat what rate the heat is produced electrically. E = line voltage, in voltsThis rate is measured in watts. The rate ofheat depends on the power that the appliance I = current, in amperesdraws from the electric circuit to produce a For most small home appliances and lamps,desired amount of heat. Therefore, heating the line voltage is 120 volts, but water heaters,appliances are rated in watts or kilowatts ranges, dryers, and other heavy equipment(1 kilowatt, or 1 kw, = 1000 watts). require 240 volts.Usually the wattage rating of a heating For example, a 3000-watt heater which drawsappliance is indicated on the nameplate. 25 amp from the 120-volt line has a resistanceSince the voltage is generally 120 volts, thecurrent drawn by the appliance can be R = E/Idetermined by dividing watts by volts.The formula is = 120/25 = 4.8 ohmsI = P/E What will happen to the wattage produced by the heater if the resistance of the heaterin which is increased? Let’s assume that the 4.8 ohm heating element is replaced by an elementI = current, in amperes which has a 10-ohm resistance. First, find howP = power, in watts much current the new element will draw from the line. You can do that by applying anotherE = voltage, in volts form of Ohm’s law, which isFor example, you may want to find the I = E/Rmaximum current a 3000-watt heater willdraw so that you can use the right size of In other words, divide the voltage by thefuse or circuit breaker in the heater circuit. resistance to get the amperes:Fuses and circuit breakers are rated in current I = E/Rvalues, such as 20 amp or 30 amp. For the3000-watt heater the current will be = 120/10 = 12 amp.I = P/E The 10-ohm element draws much less current than the 4.8 ohm element. Remember the = 3000/120 = 25 amp. rule: More resistance draws less current at theYou should select a 30-amp fuse or circuit same line voltage.breaker.
28 Electric Heating Appliances and FansNow you can find the wattage by multiplyingvoltage and current. The formula isP=E×I 120 VOLTS 400 WATTS = 120 × 12 = 1440 watts TOTAL POWER = 400 WATTSThis wattage is much lower than the wattage (a)obtained with the 4.8-ohm element. So, therule is: More resistance draws less power at thesame line voltage. 400 400 120 VOLTS WATTS WATTSNow let’s assume that the 4.8-ohm heatingelement has been replaced by a 2-ohm TOTAL POWER = 800 WATTSelement. The current drawn from the line (b)will beI = E/R 120 VOLTS 400 400 400 = 120/2 = 60 amp WATTS WATTS WATTSand the power will be TOTAL POWER = 1200 WATTSP=E×I (c) = 120 × 60 = 7200 watts FIGURE 23—This illustration shows how more heatLower resistance causes higher current and can be developed using parallel heaters.higher power at the same line voltage. parallel with the first two, as in 23(c), we getThe foregoing rules will be helpful when three times the power of one element, orreplacing and combining heating elements. 1200 watts. How can we make a variable heater usingMultiple-Heat Circuits with these three elements? By using a selector switchParallel Elements which will connect one, two, or three elements across the circuit, so that 400, 800, or 1200Let’s see how heating elements can be used watts can be produced by the combinationto get different heat outputs. Assume that of elements. As shown in Figure 24, one endwe have three heating elements, each one of each element is connected to the commonrated 400 watts. This information is on the side of the AC line. The other side of the linetag or the label on the heater. The elements is connected to a selector switch, which isare made for use on a 120 VAC line, and here of the shorting type. The movable bartherefore, if connected across 120 volts, each is connected to the hot side of the AC line.one will develop heat at a rate of 400 watts. The bar can be moved from left to right to make a connection between the powerlineIf we connect only one of the elements and one, two, or all three of the elements. Theacross the 120-volt line, as in Figure 23(a), switch is shown in the MEDIUM position.we get 400 watts. If we connect another Two of the elements are connected, while theelement in parallel with the first, as shown third is still open; thus 800 watts is produced.in 23(b), we have the same voltage across By moving the shorting bar one position toeach one and we get double the power, or the left, or to the LOW position, we would800 watts. Connecting the third element in have only one element connected in the
Electric Heating Appliances and Fans 29 If you turn the switch to the LOW position, HOT WIRE all three elements are in series in the circuit LOW MEDIUM supplied by the line voltage. The current 400 800 HIGH drops to one-third of its original value, and WATTS WATTS 1200 120 VOLTS WATTS the wattage drops to one-third of the value of one element, or 400/3 = 133 watts. If you COMMON 400 400 400 WATTS WATTS WATTS want to measure the voltage drops, you’ll WIRE find one-third of 120 volts, or 40 volts, across the terminals of each element. This equal SHORTING division of voltage and wattage works out SELECTOR SWITCH only if each element has exactly the sameFIGURE 24—Multiple heat settings can be accom- resistance.plished using a switch to select parallel heatingelements. In appliances themselves you will find elements of different wattages used incircuit, producing 400 watts. By moving multiple-heat circuits. The actual wattagethe bar all the way to the right, or to the depends on the work the appliance is sup-HIGH position, 1200 watts is produced. posed to do, and how much heat is needed in each position of the selector switch. The manufacturer can combine resistance valuesSeries-Connected Elements so that they produce exactly 100, 200, and 300 watts on the three positions, or any otherNow let’s connect two equally rated elements groups of selected wattages.in series. How much wattage will two 400-watt elements develop when connected Always remember the following basicin series? Each one of them has a certain principle: The lower the resistance of theresistance R. When we connect two equal heating element, the higher the wattage atresistances in series, we double the resistance the same voltage. In a series combination,and the current will be cut in half. The voltage as in Figure 25, the single element has theremains the same. If the current is cut in half, lowest resistance, but will be the hottestthe wattage also is cut in half. We would get one and will produce the highest wattage.200 watts, or one-half of the value of either Let’s assume, for example, that in a coiledone of the original elements. heating element of a room heater, a 10 cm (4 in.) piece breaks off at one end. If youIf all three elements are connected in series,as shown in Figure 25, a selector switch maybe added to change the element combina- SELECTORtions. The switch is not of the shorting type. SWITCHWith the selector switch in the farthest left, LOWor HIGH position, only one of the elements HIGH 133 WATTS 400 WATTSis connected in the circuit. This would give MEDIUM400 watts. Turning the switch to the middle 120 VOLTS 200 WATTSposition shown in Figure 25, or MEDIUMposition, the current has to go through bothelements connected in series. Since the resis- 400 WATTS 400 WATTS 400 WATTStance is double, the current is one-half of theprevious current and the heat is produced FIGURE 25—This illustration shows how series-with a power of only 200 watts. connected elements may be selected for varying heat output.
30 Electric Heating Appliances and Fansstretch the remaining part and connect it would be instantly melted because it wouldagain, the element will get considerably draw a very high current, develop a veryhotter, because you have taken out a part high wattage, and produce so much heatof the resistance and made it possible for that the copper wire would melt.more current to flow through the element. A simple rule will help you to rememberSimilarly, if you connected a short piece of this principle: The more wire, the less heat,wire directly across the 120 VAC line, with- and vice versa.out any fuses or circuit breakers, the wire
Electric Heating Appliances and Fans 31 ✔ Check It Out! 3 1. What current, in amperes, will flow through a 50-ohm heating element connected to a 120-volt supply voltage? _________________________________________________________________________ 2. What is the wattage obtained from a 20-ohm heating element connected to a 120- volt supply voltage? _________________________________________________________________________ 3. If a 500-watt heater operates at 120 volts, what is the current flowing through the heater? _________________________________________________________________________ 4. If a 30-ohm heating element is replaced by a 60-ohm element, how will the wattage change if the voltage remains 120 volts? _________________________________________________________________________ 5. What is the total wattage obtained from two 500-watt heating elements connected a) in parallel? b) in series? _________________________________________________________________________ Check your answers with those on page 82.
32 Electric Heating Appliances and FansELECTRIC IRONS THERMOSTATOperating Features of an HEATINGElectric Iron ELEMENTThe electric iron produces heat for pressingclothes. It has a heating element mountedin a thick metal soleplate, and the heat iscontrolled by an adjustable thermostat FIGURE 26—Simple dry, steam, or spray/steammounted directly on the soleplate. When irons use this simple electric circuit.the iron is plugged into an electric circuit,the heating element brings the soleplate up How an Electric Iron Isto the ironing temperature. The range ofironing temperatures is much higher than Constructedthe range of temperatures in small cooking The first models of electric irons did notappliances. use thermostats. The user controlled theThe iron can be set to maintain various aver- temperature by pulling out the heavy-dutyage heats for different materials. Linen, for appliance plug from the back of the iron.example, requires an iron temperature of The new irons do not use appliance plugs.260° C (500° F) or above, while rayon should The line cord is connected permanently tonot be pressed with an iron hotter than around the back of the iron, with the electrical135° C (275° F). Temperature selector readings connections made to heavy terminals insidevary somewhat for different makes of irons. the shell.Electric irons are made in dry, steam, or spray The temperature is controlled by an automaticmodels or a combination of these types. A thermostat with a built-in switch. The shell isdry iron presses clothes without using water made of heavy polished metal, with a handleor steam. A steam iron has a tank, or reservoir, made of insulating material.into which water can be poured. Sometimesthe iron has a window that indicates thewater level in the iron. The water boils, and How a Dry Iron Is Builtthe resulting steam is emitted from ventsin the soleplate. Steam ironing is done on A typical dry iron is shown in Figure 27. Thecertain fabrics in preference to dry ironing. heating element is cast into the soleplate, andSpray irons have, in addition to the steam- its electrical leads emerge through ceramicironing feature, a spray mechanism which insulators and are connected to a terminalis built in and which is actuated by pressing plate under the handle. A screw holds thea button on the top of the handle. This feature terminal bracket in place. Electrical connec-is desirable for the extra dampening of clothing tions are made by screws which hold the endsat some stages of ironing or pressing. of the element leads and the line-cord wires together. In all irons, one line-cord wire willOlder electric irons are electrically very simple. be connected directly to the heating elementThey have only one circuit which includes a lead, and the other wire will be connected toheating element and a thermostat connected one of the thermostat terminals. The secondin series to the source of voltage, as shown thermostat terminal is connected to the otherin the diagram in Figure 26. element lead.
Electric Heating Appliances and Fans 33 HEAT CONTROL ELECTRICAL-CONNECTION KNOB CORD STRAIN SCREW RELIEF HANDLE CORD LINE GUARD CORD TERMINAL NAME PLATE PLATE HANDLE SCREW SHELL WASHER SCREW SHELL SCREW CERAMIC INSULATOR SOLEPLATE THERMOSTAT THERMOSTAT SCREW HEATING CONTACTS ELEMENTFIGURE 27—This is a cross-section of a typical dry iron.The line cord is inserted into the shell An older type of dry iron is shown in Figure 28.through a hole in the back of the handle. This iron contains the same main parts inA soft-rubber sleeve serves as a cord guard practically the same locations as the iron inand helps to keep any bending of the cord Figure 27, but in slightly different shapes.to a minimum. A strain relief device holds The electrical terminals are heavy flat bars,the end of the cord to keep any pull from called bus bars. The bars are mounted on aaffecting the electrical connections. heavy bracket on top of the soleplate assembly. The holes in the top of each bar are threadedThe thermostat is mounted on the soleplate by for the terminal screws. In this iron, the linescrews and insulating washers. The control cord must be disconnected before the shellknob adjusts the thermostat contacts to move can be taken off. The bus bars go up throughthem closer together for a lower operating heat the square holes at the back end of the shell,or farther apart for a higher operating heat. as indicated by broken lines. No insulationIn this model the shell of the iron is held to is used in these square holes. The bus barsthe heavy soleplate by a single long screw. are heavy enough to stay clear of the metalThe screwhead is usually hidden by the shell, but you must always check to makenameplate, which is held down by the wide sure the this is so in the iron you are repairing.flange on the thermostat knob. This knob The line-cord protector is of the coiled-springfits on the shaft tightly. The shaft is a knurled type. You can install the cord so that it comesshaft with many fine grooves in it, which are out at either the left or the right side of thegripped tightly by small grooves inside the handle, for left-handed or right handed users.knob. The handle, made of insulating mate- The opening not used is covered by therial, is attached to the shell by screws in the snap-in plug button.side of the shell. These screws, as well as theelectrical-connection screws, can be reached The thermostat is mounted directly onby removing the shell and tipping it to one the soleplate and connected to the heatingside. element with heavy wires. One wire goes to
34 Electric Heating Appliances and Fans HANDLE REAR HANDLE SPACER CONTROL KNOB SHELL WITH SCREW SCREW FRONT HANDLE CORD SPRING SPACER PLUG STRAIN BUTTON RELIEF CORD SHELL ONLY CONTROL KNOB HANDLE RETAINER SPRING BUS BAR COVER CONNECTING WIRE THERMOSTAT (PRESET) BOTTOM COVER PLATE BIMETAL STRIP SOLEPLATE AND ELEMENT ASSEMBLYFIGURE 28—An older dry iron is shown here in an exploded view. (Courtesy of Western Auto Supply Company)the bus-bar terminal and the other to the within the range of 120° to 288° C (250° toheating element inside the soleplate. The 550° F). The indicator on the outside doesother element lead emerges from a hole in not show temperatures in degrees, but isthe soleplate and is connected to the other marked instead with the name of the fabricbus-bar terminal. for which a particular temperature is best. You’ll find markings like this: OFF, WASH AND WEAR, RAYON, WOOL, COTTON,Thermostats in Irons LINEN. Linen needs the highest heat to get a smooth press. Wash and wear materialsThe thermostats found on electric irons work and synthetic fabrics, such as rayon, nylon,in the same way as the thermostats on other and orlon, among others, must be ironed atappliances, but they are made in many differ- a comparatively low temperature. Too muchent shapes and sizes to fit particular irons, and heat can actually melt the fibers of the syntheticthey operate at higher temperatures. fabrics and ruin expensive clothing. (HoldThrough the bending of the bimetallic blade, a match to a scrap of synthetic material, andthe thermostat opens and closes a pair of you’ll see that the material actually meltselectrical contacts and keeps the temperature before it burns.)
Electric Heating Appliances and Fans 35 The heat setting of this thermostat is adjust- able by turning the shaft (6). The shaft is threaded and has a metal bushing that is threaded to raise and lower the shaft as it is turned. The lower end of the shaft rests upon a small pad of insulating material on the contact assembly. The whole contact assembly, together with the lower contact arm (7), is moveable. The shaft bushing has left- handed threads; when the knob is turned clockwise, the shaft rises, allowing the contactFIGURE 29—These are the components of a assembly to rise away from the arm stop.typical iron thermostat. The bimetallic blade has to bend more to open the electrical contacts and, therefore,A typical iron thermostat is shown in Figure 29. the iron gets hotter.The bimetallic blade (1) is at the bottom of thethermostat assembly. This blade does not When the heat-control shaft is turned counter-carry electric current, and it’s grounded to the clockwise, the shaft lowers and the contactsthermostat mounting bracket. It is mounted will open at a lower temperature value.so close to the tip of the soleplate that direct If the shaft is turned completely counter-radiation of heat causes it to operate. The clockwise, the contact arm assembly is pushedsmall arm stop (2) is attached to the end of down so far that the upper contact arm hitsthe bimetallic blade. This piece is made of the arm stop and forces the contacts to stayinsulating material and is used to operate the open. This is the off position of the adjustingupper contact arm (3). knob.When the iron is cold, the thermostat blade The thermostat has a shaft stop (not shown)is pulled down towards the soleplate. The which prevents the shaft from turning morethermostat’s contacts are closed. When than about 270 degrees, or about three-quartersvoltage is applied, the blade absorbs heat of a full turn. Irons that have the thermostatand bends up and away from the soleplate. control knob set into a slot at the front of theThis action raises the insulated stop up handle may turn only half a turn, or aboutagainst the upper contact arm and raises it. 180 degrees. The main parts of the thermostatWhen this arm is raised high enough, the shown in Figure 29 are shown in the diagramelectrical contacts (4) open, breaking the of Figure 30.electrical circuit to the heating element in Thermostats in electric irons must be replacedthe soleplate. with exact duplicates. If you were to replace aAs the iron cools, the bimetallic blade bends thermostat that turns 270 degrees with adown, lowering the arm stop along with thermostat that turns only 180 degrees, itthe upper contact arm. When the iron has would not work properly. It would controlcooled enough, the contacts touch and the the temperature over only a part of the range,circuit to the heating element is again closed, and the user would not know how to setallowing the iron to heat up. An insulated wire the temperature, because the dial markings(5) can be seen attached to this thermostat. wouldn’t match the thermostat. This is notSome irons, especially older ones, will likely to happen, however, since the wronghave thick metal buss bars instead of wires. thermostat would not normally fit into the mounting brackets.
36 Electric Heating Appliances and Fans HOTTER KNURLED SHAFT FOR KNOB LEFT-HAND THREADS MOUNTING BRACKET HOTTER COLDER UPPER HOTTER LOWER CONTACT INSULATED CONTACT ARM STOP COLDER BIMETALLIC BLADEFIGURE 30—The set point of an iron thermostat is adjustable by means of this mechanism.Steam Irons are usually formed as small, oval-shaped, countersunk holes so that the steam canSteam irons are built in the same way as dry escape through the fabric more easily. Theirons, except that they contain a water tank holes are set around the tip of the iron, toand steam pipes. They can be used as dry let the steam dampen the fabric before it isirons by simply leaving the water tank empty. pressed by the iron. Then the larger back part of the iron passes over this area andA cross section of a typical steam iron is smooths out the wrinkles.shown in Figure 31. The soleplate containsthe heating element, which is controlled bya thermostat. The shell is usually larger thanthe shell of dry irons because it contains a Spray Ironswater tank. The water is heated well above Spray irons produce steam in the same waythe boiling point, which is 100° C (212° F), as steam irons, but, in addition, they sprayto a soleplate temperature of about 177° C water on the fabric from a tiny nozzle at the(350° F), with the result that the water is front of the handle. A typical steam-spraytransformed into steam. iron is shown in Figure 33 on page 38. ItThe steam is taken off through a vent pipe, has the same type of thermostat and heatingwhich is installed so that its top is always element as the steam iron, but the tank isabove the water, and only steam can go slightly larger.through it. The pipe is connected to a set of The spray nozzle is at the front of the handle.small vent holes in the soleplate, as shown It is connected to a miniature pump with ain Figure 32. The holes are fairly small and small bellows inside the front post of the
Electric Heating Appliances and Fans 37 PIPE STEAM WATER HOLESFIGURE 31—One method of creating steam is shown here. (Courtesy of Omar Appliance Manufacturing Company)handle. When the SPRAY button on topis pushed down, the bellows is compressedand forces a small amount of water throughthe nozzle onto the fabric just before theiron goes over it.When the button is released, a small springbrings it back up, opening the bellows.When this happens, the suction createddraws water from the tank up into thebellows for the next spray. A check valvebelow the bellows allows water to flowup into the bellows, but won’t let it goback into the tank when the button ispushed down. You’ll find several vari-ations of this system, some using asmall piston and cylinder pump, butthe action is the same. FIGURE 32—The steam holes are located in the soleplate of steam irons.
38 Electric Heating Appliances and Fans THERMOSTAT SPRAY BELLOWS CONNECTOR (POSITIONED IN SPRAY BUTTON ROD CAM FOLLOWER SPRAY LEVER) BELLOWS CLAMP YOKE SPRING NUT ADJUSTING NUT CONTROL LEVER SPRING CALIBRATING SCREW COVER ASSEMBLY YOKE ASSEMBLY MOUNTING SPRAY ASSEMBLY NUT MOUNTING BRACKET SPRAY NOZZLE VALVE CUP FILL OPENING GASKET FLAG THERMOSTAT CLAMP CONTACT ARMS INSTALL BLADE WITH "STAR" LOCK WASHER UP COVER VALVE VALVE GASKET MOUNTING STEM BODY BRACKET ASSEMBLY COVER MOUNTING SPACERFIGURE 33—Spray irons allow both steam and spray operations in one iron. (Courtesy of Westinghouse Electric Corp.)Check Valves through the hole. The pressure from below lifts the ball up and opens the hole. WhenYou will find check valves used in all spray the pressure is reduced, the ball is pushedirons, and in several other appliances as well. back into the hole by the spring and closesThey permit a liquid or a gas to flow in one the valve. The higher the pressure on thedirection, then prevent its return; thus, they top, or on the ball side of the valve, the harder“check” the return flow. the ball is forced against the seat, and the tighter it seals the hole.The two most common types of check valvesare shown in Figure 34. The size and type The opening of the valve can be determinedused will depend on the operating tempera- by the spring tension. The valve will not openture and on whether gas, air, or liquid must until the pressure from below is greater thanbe controlled. In spray irons, you will find the pressure from above, due to the tensionthe type of valve known as a ball check valve. of the hold-down spring. In spray irons, theThis valve is shown in 34(a). pressure from above is very low because the spring is very weak. However, the springThe ball valve uses a small metal ball which tension is easily adjusted by the screw aboverests in a tapered seat above the tank. The the spring. The tension is raised by turningactual opening, or hole, is in the center of the screw farther down. The valve can bethis seat. A spring holds the ball against the made to stay closed until a certain pressurehole. When pressure is applied from below has been built up below it.or suction from above, liquid can flow up
Electric Heating Appliances and Fans 39 The second type of check valve, shown in Figure 34(b), is also a one-way device; it is TENSION used for very low pressure applications. ADJUSTMENT This valve is quite simple. It consists of thin plastic or rubber flaps placed over a hole and fastened at only one side. The liquid below the valve can easily lift the light flap and rise through the hole. The return flow SPRING TAPERED makes the flap fall back and close the hole. SEAT BALL HOLE TANK (a) FLAP COVERING FLAP RAISED HOLE HOLE FASTENED EDGE (b)FIGURE 34—Check valves, such as those shownhere, are used to prevent a reverse flow of water.The ball type of valve serves as a safetyvalve when used on water heaters and boil-ers, to keep them from exploding. The valveis set to open at a pressure well below thebursting strength of the boiler or heater. Ifthe pressure becomes dangerously high, thevalve will open and let out excess steam.
40 Electric Heating Appliances and Fans ✔ Check It Out! 4 1. Where is the heating element mounted in an electric iron? _________________________________________________________________________ 2. What is the main difference in construction between a dry iron and a steam iron? _________________________________________________________________________ 3. Where is the thermostat mounted in an electric iron? _________________________________________________________________________ 4. How many electric circuits are there in an older electric iron? _________________________________________________________________________ 5. How is the line cord attached to an electric iron? _________________________________________________________________________ 6. What is the position of the thermostat blade when the iron is cold? _________________________________________________________________________ 7. What is the purpose of the vent pipe in an electric steam iron? _________________________________________________________________________ 8. What is the purpose of the ball in a check valve? _________________________________________________________________________ 9. Why is an exact factory duplicate necessary to replace a thermostat? _________________________________________________________________________ 10. What are the two common types of check valves? _________________________________________________________________________ Check your answers with those on page 82.
Electric Heating Appliances and Fans 41 and the circuit is broken. This is the cause ofHOW TO TEST AND the user’s complaint that “it heats up one timeREPAIR ELECTRIC IRONS and does not heat up the next.” How to Repair the Line CordTesting the Line Cord To repair the cord when the break is at theThe electrical testing of irons is very simple plug end, cut the line cord about 5 cm (2 in.)because the irons have only three main from the plug, strip the wires, and replace theelectrical parts: the heating element, the plug. Be careful to use a heavy-duty replacementthermostat, and the line cord. You can use plug so that it will not heat up or burn upthe same tests you learned to perform on when approximately 1000 watts are usedthe other heating appliances which you have by the iron.been studying. If the iron does not heat up,it has an open circuit in one of those three If the break in the cord is at the end going intoparts. You can find out very quickly which the iron handle, cut the cord past the break, strippart is open by making the proper tests. the wires, put terminal lugs on the ends, and reinstall the cord. Use stripped wires of theFirst make the external tests to avoid unnec- same length as on the original cord.essary opening of the iron. A continuity testshould be made first. Most troubles with At the iron end of the cord, there is a strainirons are due to a faulty line cord. As the relief, such as shown in Figures 27 and 28.iron is moved back and forth during ironing, It has the form of a small metal loop, or clip,the cord is bent, pulled, and continuously around the cord at the point where it goesflexed. It is quite apt to break, one strand through the hole in the handle. It protects theat a time, until the last one breaks. Then the line cord from mechanical strain. There williron won’t work. You’ll find a much higher be a small piece of heavy gray paper, calledproportion of line cord breaks in irons than fish paper, placed as insulation between thein other appliances where the line cord is metal clip and the cord itself. Hold the clipseldom moved. in a pair of pliers and pry it open with a screwdriver blade. Take the clip off the oldMost of the cord breaks will be near the cord and clamp it over the new one at a pointends of the cord, either at the line plug or where it will be sure to keep the pull off thenear the iron handle. As a quick check of electrical connections. Squeeze the clip tightlythe line cord, perform a continuity test with with the pliers until it has a firm grip on thethe digital VOM across the prongs of the line cord.cord at the plug. If the meter shows normalresistance, grasp the cord near the line plug, If cutting the line cord will make it too short,and move it back and forth in all directions. replace the entire cord with a new one. YouWatch the meter to see if it suddenly reads can get ready-made cord sets for electric irons,an open circuit as infinity ohms or overload. with terminal lugs, a strain relief, and a soft-If it does do so at a certain position of the rubber or spring cord protector. If you don’tcord, you have found the intermittent break have a new iron cord in stock, you can alwaysin the cord. cut the appliance plug off a cord set and install lugs. This, however, is only an emergencyWhen you move the cord, the broken ends measure. You should have a few line cordstouch and complete the circuit, and the iron of each type in stock, because replacing a lineworks for a moment. But when you pull the cord will be one of your most frequent jobs.cord a certain way, the ends are pulled apart,
42 Electric Heating Appliances and FansHow to Take a Steam Iron the handle assembly next and tighten down the two retaining screws. Finally, replaceApart the nameplate.In newer irons, ordinary screws are used Not all steam irons are made exactly liketo hold the shell and the soleplate together. this one. The exploded view of a similarThey are easy to remove compared to the steam iron is shown in Figure 36. After youfittings and latches on older models. open this iron, following steps similar to those shown in Figure 35, you will have toWhen taking apart the steam iron shown in pry out the water-tank filler, which fits inFigure 35(a), first remove the small plate that a hole in the front of the handle. The holecovers the front of the handle. To remove this leads to the tank-filler neck on the top ofplate, pry it up gently with a small screw- the water tank. The check valve in this irondriver. Next, remove the handle screw and is the small rod that works in the same waya screw at the rear of the iron. These screws as the ball check valve. It has a rounded tippass down through the handle and shell, and which is pushed up into a tapered seat insidethread into the soleplate. Once the screws are the filler neck, keeping the water from goingremoved, remove the handle assembly. back but making the steam turn down throughFigure 35(b) shows how the shell can then the steam pipe, to emerge through the holesbe lifted from the iron. If you want to remove in the soleplate.the shell completely, you will have to remove When you take an iron like this one apart,the two wires. One wire connects to a heating make careful notes about the exact positionelement terminal while the second wire and mounting of each part if you don’t haveconnects to the thermostat. a special service-data folder for the model.To put the iron back together, reverse the Also make rough sketches of parts and theirdisassembly process. Replace all wires then original position; it will save time when youplace the shell over the soleplate. Replace start to put them back together. (a) (b)FIGURE 35—These are the steps in the disassembly of a steam iron.
Electric Heating Appliances and Fans 43 WATER- TANK FILLER LINE CORD DIAL COVER TENSION PLATE WASHER THERMOSTAT CONTROL CONTROL NAMEPLATE LEVER NUT SHELL TANK- CHECK FILLER VALVE NECK SCREWS WATER TANK SHELL THERMOSTAT BRACKET CONTROL SHAFT STEAM SCREWS PIPE THERMOSTAT BACK PLATE SOLEPLATE Courtesy of Western Auto Supply CompanyFIGURE 36—A second type of steam iron is shown here.
44 Electric Heating Appliances and FansThe thermostat in this iron is controlled by a the shaft by a small screw in the center.lever at the top front of the handle. A long, When this screw is taken out, the knobflat shaft fits through a slot on the inside pulls off easily. The hold-down screws fitend, and the lower end fits into a slot in the into threaded holes in a small metal bracket,thermostat. To reassemble this part, the which in turn is screwed down to the sole-shaft is slipped into the slot in the thermo- plate, over the thermostat connections. Youstat, and the handle is carefully lowered must disconnect the line cord from the endsover it and properly placed. Before the shell of the bus bar terminals. The bus bars willis seated all the way, the thermostat control not go down through the holes after the shelllever and the tension washer are slipped has been loosened, until the line cord andinto the slot in the front of the handle. The screws have been taken off.lever is carefully worked back and forthuntil the end of the control shaft fits properly On some irons, electrical connections to theinto the slot. Then the shell can be pushed cord terminals are not made with screws butall the way down. The thermostat dial is a with push-on connectors, which are smallhalf-moon shaped plastic piece. It is pushed spring-clip devices on the ends of the lineinto the slot and held tightly by the pressure cord wires. They slip over matching metalof the tension-washer springs. tongues at the ends of the bus bar. An insu- lating sleeve slips over the connector to keep it from shorting to other wires or to otherHow to Take Dry Irons Apart metal parts. These connectors are used on many appliances, and they make the assem-In the dry iron shown previously in Figure 27, bly and testing much easier than screws orthe shell is held down by one long screw. soldered terminals.To reach this screw, you must remove theheat-control knob. Pry up the knob on thesides at the same time with long, thin screw-driver blades. Do no use too much force, Continuity Test of Heatingbecause the knob can break easily. If the Element and Thermostatknob won’t come off, use wider and flatter After you have removed the shell, you cantools, such as a pair of putty knives, so that make quick electrical tests of the element andyou can apply the pressure at the same time the thermostat. One way is to clip one of theover as large a surface of the knob skirt as leads of your digital or analog VOM set aspossible. an ohmmeter to the thermostat connectionAfter the knob is lifted, the nameplate can leading to the element. Then you can touchbe gently pried out. Then the shell screw the other test clip to the other end of thewill be visible. element, or to the other side of the thermostat. In only two moves, you can test both of theseIf you have taken out all the exposed screws, parts for continuity. Since this continuityand the shell still remains tightly in place, test is made with no voltage supplied, it isdon’t try to pull it off by force. Try to find safe and it can be done fast.the remaining screws, which may be con-cealed under an ornament, a nameplate, a The average heating element in an irontrademark, or a snap button. rated 1000 to 1200 watts will normally have a resistance of 10 to 15 ohms. If theThe iron shown previously in Figure 28 is meter reads 10 to 15 ohms across the heatingmade somewhat differently. The shell is held element terminals, the element is in goodon by two small Phillips screws under the working condition. No resistance indicatesthermostat knob. The knob itself is held to an open circuit.
Electric Heating Appliances and Fans 45Across the thermostat contacts the meter for this purpose. Never use plastic tape on thereading should be zero resistance (dead inside of an iron.short) with the thermostat set to one ofthe many heat settings.If you read any resistance across the thermostat How to Remove Bolts andcontacts, they are not making good contact. Nuts from an Electric IronThey are probably dirty and must be cleanedor replaced. Examine the contact surfaces; if The repeated heating and cooling of the ironthey are badly pitted and burned, insert a new parts causes the nuts and bolts to oxidize, orthermostat. No resistance reading across the rust. They are often “frozen,” that is, verythermostat contacts indicates an open circuit. hard to loosen. You should try to removeCheck the position of the shaft to make sure them without damaging any parts that willthat the thermostat isn’t in the OFF position. be used again. No damage is done, however,If the thermostat has a slotted shaft, you if you break a faulty element or thermostatcan turn it with a small screwdriver. If it which would have to be thrown away inhas a knurled shaft, you can slip the knob any case.back temporarily, so that you can turn the Removing frozen bolts and nuts oftenthermostat to a point where you know it is requires force and special tools. AlwaysON. Anywhere in the middle of the range remember the following rules:should be ON. You can also check whetherthe contacts do open when they should. With 1. The body or main part to which somea VOM connected across the thermostat other parts are attached must be heldterminals, turn the control lever all the way tightly but without damaging it.to the left, or to the OFF position. The contactsshould open and the resistance should drop 2. You must be careful how you applyto open, or an infinity reading, when the force.lever reaches the OFF position. This is a For example, don’t twist a nut screwed ontouseful test which should show that the a stud on the soleplate too much; if you do,thermostat contacts are not welded together you can easily break off the stud. Then you’lland stuck. have the long, hard job of drilling out theBecause of the way the steam irons are broken piece and rethreading the hole for amade, you will find it easy to trace the new stud.electrical connections. They are made When working on irons, you will find thatwith very heavy wire, flat strips, or bus most of the hard-to-remove parts are mountedbars. Only three connections in the whole on the heavy soleplate. You can hold theiron circuit have to be checked, and they soleplate in a vise and place some paddingare easy to identify. They are between the between the jaws so that you don’t scratchheating element, the thermostat, and the the soleplate. Another way is to use twoline-cord terminals. In many irons electrical C-clamps, as shown in Figure 37, to hold theconnections are made with bus bars so soleplate unit to the edge of the bench. Put aheavy that they are mounted without thin pad of cloth between the polished sole-insulation between points which have to plate and the bench top. Set the C-clamps sobe connected. They stay free of contact with that the handle is down; this keeps the handleother parts because they are rigid. If any out of the way while you are working. If youinsulation is used, it must be of the high put the soleplate at a corner of the bench, youtemperature type because of the very high can use two clamps to hold it tightly in place.temperatures. Fiberglass tapes are available
46 Electric Heating Appliances and Fans To check for the presence of scale, fill the tank with water and heat the iron. Most steam irons have a steam valve which has a push button at the front, on top of the handle, so that the user can operate it with his or her thumb. The steam valve is made with a small notch on the front of the button; when the button is pushed down and forward, it latches and stays down. This is the DRY position of the iron. To start the steaming, push down on the button, pull it back, and release it. This will let the button pop up and open the steam valve. The thermostat- control lever must be in the STEAM position,FIGURE 37—The soleplate of an iron can be held usually near the center of the range.firmly to your workbench by using “C” clamps asshown here. After the iron has heated, lift it off the table, holding it in the normal working position, with the soleplate horizontal. Watch for smallHow to Detect Scale in puffs of steam coming out of the vents in theSteam Irons soleplate. Older irons will steam when set upright on the heel, but the new ones won’t.The steam iron boils water to produce steam. If you can’t see the steam, run the iron overThe steam boils off as pure water, and any a piece of clean, dry cloth, then feel the cloth.chemicals present in the water remain behind If the iron is steaming properly, the clothin dry form. Most tap water has various should feel warm and damp. If the ironchemicals dissolved in it. These are not does not steam, it needs cleaning.harmful to people, but the deposits theyleave in the clean iron can cause trouble. Drain the water out by holding the iron, withThe more chemicals, such as calcium, that the front downward, over a sink. Let it cool.are dissolved in the water, the “harder” the Then check the steam vents in the soleplate.water. Very hard water will clog up a steam You will detect the scale as a crust on theiron in a short time. Most of the instruction inside of the holes.booklets that come with the steam ironsrecommend the use of distilled water, butonly a few owners use it. Therefore, you’ll How to Clean Steam Ironsoften find steam irons which need cleaningout. You can clean practically all steam irons without taking them apart. This is done withThe deposit left by the water is called scale. a special chemical cleaner which dissolves theIt forms a hard, light-colored crust on the scale. A mild acid is the most common type.inside of the tank, in the tiny tubing, vents, You’ll find several kinds of cleaners in hard-and valves. After a while this scale can get ware stores and catalogs, under differentso thick that it clogs the vents, and the iron trade names, but they will all have the wordswon’t steam any more. When the user com- “Steam-Iron Cleaner” on the label.plains that “The iron gets hot but it won’tsteam any more,” this is often the cause. First, read the directions on the bottle of cleaning fluid. Most cleaners are concentrated, and a certain amount of the liquid is mixed
Electric Heating Appliances and Fans 47with water before putting it into the steam holes in the soleplate. Use a bit size that justiron. Make the mixture according to the barely fits inside the hole.directions, then set the iron over a large pan,or on a rack over a sink. Pour the cleaner Many of the steam valves will have a taperedinto the iron, with the steam valve in the seat, with a blunt-pointed tip on the valveSTEAM position. Most of these cleaners stem. Take a piece of very fine sandpaper orwill be poured into a cold iron; check the crocus cloth (a very fine emery paper) and folddirections to make sure. With the steam valve it between your fingertips. Then, twist theopen, the fluid drips through the vents and valve stem inside the sandpaper until it be-into the sink. While it is inside the iron, it comes very smooth and polished. If thedissolves the scale so that it can be flushed valve seat is corroded, take a very small bitaway. and polish the seat slightly by twisting the tip of the bit in the hole. If the valve seat isIf the iron is very badly clogged, you may so badly corroded that it leaks after thehave to repeat the treatment until the vents cleaning, replace it with a new one.are clear and the iron steams as it should.After the treatment is finished, rinse theinside of the tank with clear water. Fill the Disassembling Newer Ironstank with water, shake the iron vigorously, Modern irons, like the one shown in Figure 39,and then pour the water out by holding the contain many features such as temperatureiron over the sink. The cleaners have an indicators, self-cleaning steam systems, andadded coloring agent. Flush the iron until electronic auto shut-off. Construction detailsthere is no trace of color in the water as it for these irons are quite different than thepours out. While this color is not harmful, older irons. This is especially true in the useit could cause staining of clothes if some of plastics for the handles and shells of theseof it is left in the iron. irons. It is highly recommended that before youIf the iron is still clogged even after a couple begin to disassemble a modern iron with theof treatments with the liquid cleaner, you’ll above-mentioned features you acquire ahave to take the iron apart and check for service manual for the specific iron you areclogged valves and tubes. The spray-steam working on.iron shown in Figure 38 has a tiny pump, a The disassembly of a newer iron usuallyvalve stem, and tubing which you will find begins by removing the line cord cover andin many irons. You can push a small, stiff wire the nameplate. The line cord cover on newerthrough clogged tubes to clean them. If this irons usually is attached by a screw that isdoes not help, take the clogged valves apart of the non-standard screwhead type. Onceso that the scale can be scraped out. Be very the screw is removed, the line cord covercareful that you don’t damage the tiny parts. plate can be removed by gently pulling itOne handy way of opening up clogged away from the shell and handle assembly.tubes is to use a small drill bit. Hold it in Once the rear cover is removed, unhookyour fingers and push it into the tubing, the leads from the power cord.twisting it clockwise. Pull the bit out every The nameplate or temperature indicator platetwo or three turns, and tap the tubing on can then be removed by gently prying itthe bench to get the loosened scale out. If from the shell assembly. Usually, you willthe bit is too short to go all the way through find Phillips-type screws holding shell andthe tube, clean out one end first, then the handle to the soleplate. One screw will beother end, and repeat the process. Small in the line cord connection area, and thedrill bits can also be used for cleaning vent other two screws beneath the nameplate.
48 Electric Heating Appliances and Fans SPRAY BUTTON STEAM LEVER ASSEMBLY CORD PISTON SPRING CAM RETAINER WASHER RIVET TEMPERATURE CAM HANDLE PLATE RING SHELL CLAMP CAM FOLLOWER PUMP SPRING PUMP AND NOZZLE ASSEMBLY NOZZLE SCREEN VALVE STEM INSULATOR AND NEEDLE THERMOSTAT AND VALVE SWITCH ASSEMBLY BRACKET GASKET TANK STEAM CHEST COVER SOLEPLATE AND HEATING ELEMENT ASSEMBLY Courtesy of Sunbeam CorporationFIGURE 38—A disassembled spray-steam iron is shown here.
Electric Heating Appliances and Fans 49 Once these are removed, the shell and handle assembly can be gently lifted from the sole- plate. A plastic insulator in the shape of the shell will then be easily lifted from the soleplate. This insulator is made of a special high-temperature plastic that protects the shell from excess heat. Once these items are removed, you will notice some difference from the older model irons. The first difference is the use of a thermal link, or thermal fuse, on the soleplate. This thermal link, or fuse, is placed in series with the line cord, thermostat, and heating element. Its purpose is to remove power from the heating element in the event that the thermostat sticks and the soleplate reaches an excessiveFIGURE 39—A side view of a modern iron is temperature. A thermal fuse is shown as itemshown here. (Courtesy of Sunbeam Corporation [Canada] 32 in Figure 40. If this situation occurs, youLimited) will have to replace both the thermostat and the thermal link. A thermal fuse will normally reset itself after the iron cools. The circuit for this type of iron is shown in Figure 41. 9 1 5 7 2 3 16 4 6 10 11 23 8 13 12 24 14 17 15 19 18 25 20 27 21 28 29 31 26 22 30 32 33FIGURE 40—This exploded diagram reveals the difference between the older and newer irons. Both typeswill usually make up a portion of your business. (Courtesy of Sunbeam Corporation [Canada] Limited)See page 84 for key to parts.
50 Electric Heating Appliances and FansDepending upon the model and make of Troubleshooting Moderniron, you will also find various other wiringconfigurations. Auto shut-off and tempera- Ironsture indicating models will have wires lead- The troubleshooting procedures for moderning from the power cord through the handle irons are very similar to those given pre-assembly and back down to the heating ele- viously. The power cord should be checkedment, thermal link, and thermostat. In the for continuity by using the resistance scalesmodel shown in Figure 40, a printed circuit of your VOM. Next, the circuit for the ther-board, 13, connects between the line cord mal link, or fuse, and the thermostat can beand thermostat, fuse, and heating element. tested for continuity. The line cord, thermal link, and thermostat should all show nearThe temperature indicating models may have zero ohms. The heating element should reada double-pole, single-throw thermostat that around 10 to 15 ohms depending upon theopens the circuit to the heating element, and model.closes the circuit to the indicator lamp whenthe soleplate reaches the set temperature. The troubleshooting of the electronic circuits should be performed in accordance with theThe auto shut-off models use an electronic procedures given in the service named fortimer circuit and a special switch to sense the particular iron you are working with.when the iron has been lifted on its heel for However, if the iron you are working withan extended period of time. Once the circuit has a mechanical action thermostat similartimes out, a relay is enabled, or a solid-state to the irons you have seen previously, youdevice is disabled, to turn the iron off. can usually bypass the auto shut-off circuit with a jumper to check the heater, thermal link, or thermal fuse, and thermostat. If the iron contains a semiconductor temperature sensor, bypassing is not suggested. THERMAL Many modern soleplates are using a non-stick LINK THERMOSTAT coating on the soleplate surface. Where older steel soleplates could be polished if scratched, HEATING the newer surfaces cannot be easily repaired. LINE CORD ELEMENT In fact, buffing or polishing with an abrasive will actually destroy the coating. If the soleplate is heavily scratched, it will require replacement. You may want to suggest to your customer not to iron overFIGURE 41—Many modern irons use a thermal zippers, buttons, and other sharp or metaliclink as a safety device against overheating. objects.
Electric Heating Appliances and Fans 51 ✔ Check It Out! 5 1. Why are most faults found near the ends of the iron line cord? _________________________________________________________________________ 2. How can you reach the line cord terminals for testing? _________________________________________________________________________ 3. What is the advantage of using push-on connectors? _________________________________________________________________________ 4. What resistance reading indicates dirty thermostat contacts? _________________________________________________________________________ 5. What is the common cause of the clogging of holes in a steam iron? _________________________________________________________________________ Check your answers with those on page 82.
52 Electric Heating Appliances and FansELECTRIC FANS 11 10 8Types of Fans 6An electric fan is used to circulate air in a 13room. Fan blades mounted on the shaft of 14an electric motor produce a current of air. 5 7Depending on the position of the blades andthe direction of motor rotation, a fan can blow 4air into a room or exhaust air from a room.The use to which a fan will be put determines 1 3the shape and size of the fan blade and the 2housing. A small fan used on a desk ormounted on a wall has a heavy metal base. FIGURE 43—A through-wall fan is used to moveThe blade and the motor are mounted on air from one room to another room. (Courtesy of Nautilus)the base and are surrounded by a round See page 84 for key to parts.guard, or cage, made of steel or plastic.This guard protects users from getting their Some medium-sized fans are built in boxlikefingers caught in the rotating blade. A small housings with mesh or wire grilles at the frontdesk fan is shown in Figure 42. It can be piv- and at the back. These may be installed inoted on its base and the fan can be tilted up windows. Some fans have reversible motorsor down to direct the air where it is needed. and can blow air into the room or out of the room, as desired. Many kitchens have fans BLADE built into special housings and placed in openings in walls, in ceilings, or in hoods GUARD over built-in stoves to exhaust the hot air and cooking odors. Large fans are mounted MOTOR- in attics or at tops of stairways to help MOUNTING circulate the air throughout the house. BOLTS One type of wall fan is shown in Figure 43. This fan is used to move heated or cooled HUB air from one room to another room. MOTOR Some fans have a gearbox mounted on the back of the motor. The gears drive an MOTOR arm-and-lever arrangement which moves SHAFT the fan from side to side to spread the HINGE stream of air around the room. Such fans BOLT are called oscillating fans. Many modern homes have combination BASE heater/light/fan units in the bathroom. BLADE These units have individual switches so that the fan can be used to vent excess mois- ture, the heater can be turned on to warm the room, and the light can be illuminated.FIGURE 42—A small desk fan is shown in thisillustration.
Electric Heating Appliances and Fans 53 Whatever the size or the shape of a fan, its main parts are the blades and the motor. The blades are the only moving part and the motor and switch are the only electrical parts. This simple construction makes the servicing and repair of fans very easy. How Fans Are Built The major parts of a medium-sized box fanFIGURE 44—This fan assembly is used in a bath- are shown in the exploded view in Figure 46.room to provide heat, light, or venting of the The rectangular sheet metal case houses thebathroom air. (Photo Courtesy of Nautilus) blades and the motor. The front and back protective grilles cover the unit completelyAll three sections of these units can be on at and support the motor and the blades.the same time. The heater section of these Medium and large fans use induction motorscombination units is normally in the range which can develop enough power to turnof 1300 to 1500 watts with its own fan to the large blades. In large, round fans a heavy,force the heated air from the unit. Figure 44 round clamp holds the motor to the guard,displays such a combination unit, while and the base and the hinges are attached toFigure 45 displays a similar fan/light unit the guard itself. In floor fans on heavy stands,without a heater/fan assembly. the stand is usually attached to the heavyLarge fans, called blowers, are used on guard rather than to the motor itself.furnaces. They have enclosed blades andoperate in the same way as the blowers in hairdryers. A blower usually has a squirrel-cage Fan Bladesimpeller built into a separate housing. Thedriving motor is mounted on top of the For small and medium fans, the blades arehousing and turns the impeller by a belt. stamped out of aluminum, or molded from plastic, to make them very light. The blades are shaped and bent so that each blade makes the same angle with the motor shaft. Aluminum fan blades are riveted or welded to a hub, or a cylindrical metal unit which has a hole the same size as the motor shaft. Molded plastic blades will be molded with the hub as a unit. In most fans, the hub is attached to the end of the motor shaft with a setscrew which fits through the hub’s side to clamp the hub very tightly to the motor’s output shaft.FIGURE 45—This fan assembly will provide a bath-room with both a light and a venting fan. (PhotoCourtesy of Nautilus)
54 Electric Heating Appliances and Fans HANDLE SCREW SWITCH BACK CASE GRILLE HINGE BLADE FRONT GRILLE HUB RUBBER FOOT LINE CORD SCREW SCREWFIGURE 46—A box-type fan contains the components shown here.On most small fans, the hub and the bladesare rolled over a shoulder machined on thehub. The hub is shown in Figure 47 before SHOULDERthe blades have been attached. The shoulderfits snugly in a hole in the center of the blades.The thin shoulder is then rolled out and downover the edges of the hole, to hold the thin SHOULDERblade tightly, as shown in Figure 48. The SETSCREWrolled shoulder acts as a hollow rivet andis called a riveted blade. A similar type of fandoes not use the central shoulder. Instead,the hub is made shorter and wider, and theblades are held to it by four rivets spacedequally around the hub. FIGURE 47—Metal fan blades are connected to the motor using a hub like the one shown here.
Electric Heating Appliances and Fans 55 BLADE SHOULDER HUB BLADE ROLLED BLADE OVER RIVETS BLADE (a) Top view ROLLED RIM BLADE BLADE SETSCREW HUB SHAFT (b) Side viewFIGURE 48—The two methods of mounting metal blades to a hub are shown here.Two- and Three-Speed Fans The simplest method of speed control is to add resistance in series with the motor. TheQuite a few of the better fans are equipped added resistors are called dropping resistorswith two-speed or three-speed motors. The because they cause a drop in voltage. Thedifferent speeds allow the user to select the voltage drop across the resistor reduces theamount of air movement. The first variable- total voltage, and the motor slows down.speed fans used a large tapped coil, or The switching circuit of a typical three-speedinductor, which was switched in series with fan with resistance speed control is shownthe motor windings. This construction was in Figure 49(a). A resistor with a tap in thequite bulky and expensive; the selector center is inserted in the motor circuit byswitches at that time were not too reliable using a switch. To prevent scorching, theeither. Modern fans use one of three methods leads and the connectors should be keptof speed control. away from the resistor. All of the resistance is
56 Electric Heating Appliances and Fans RESISTOR YELLOW (MEDIUM) MOTOR (HIGH) OSCILLATING BLUE (LOW) RED CORD SWITCH A-C LINE BLACK (a) Three-speed control with resistor BLACK RED (LINE) (HIGH) BLUE (LOW) SWITCH BLACK WHITE BLACK A-C LINE FIELD COILS FIELD COILS WHITE WHITE BLACK (b) Two-speed control with two pairs of field coilsFIGURE 49—Two common methods of fan speed control are shown here. (Courtesy Westinghouse Electric Corp.)switched in for the slowest speed, and only remember from previous studies, lost orpart of it for medium speed; all resistance wasted power in an electric circuit turns intois taken out of the circuit for high speed. heat. The resistor is, therefore, made heavy enough to handle the maximum currentThe resistor dissipates power, of course. without overheating. The resistor is usuallyWhile the resistor is in the circuit, the power mounted inside the base of the fan to keep itis divided: one part of it is used up by the as cool as possible and away from possiblemotor, and the rest must be deliberately contact by the user.wasted across the resistor. As you may
Electric Heating Appliances and Fans 57The second speed control method uses a screwdriver or Allen wrench to loosen thespecially wound motor with extra field coils, setscrew in the hub of the blade, and long-or a multiple-winding motor. The coils can be shaft nut drivers of the right size to removeswitched in and out to make the motor act the motor-mounting nuts.as a two-pole or four-pole motor. Thusdifferent speeds are obtained. The greater Later models of desk fans have a guard madethe number of poles, the lower the speed. The with more closely spaced rods than the earlierswitching circuit of a two-speed fan is shown models. The guard is usually made in twoin 49(b). When you trace the circuit, you will halves. The front half is locked to the backfind that the switch connects either one pair by hooks formed in the guard rods. Theseor two pairs of field poles in series. Some three- hooks slip inside the rim and are snappedspeed fans of this type have as many as six into place by spring tension. To remove theseparate field coils; they are switched in and front part of the guard, gently pry the rimout in various combinations for any desired forward with a screwdriver until the hooksspeed. slip free. Now the blades are exposed, and you can take out the setscrew and reach theThe third method of speed control, which mounting nuts to remove the motor. Theis increasing in popularity, is electronic speed motor is mounted in the loops formed in thecontrol. It uses an electronic device called a guard rods, as shown in Figure 50. In mostsilicon-controlled rectifier, or SCR, which is desk fans, you can remove the motor and thesmaller and cheaper than other control blades together. Take the motor-mountingdevices. nuts off with a long, thin, open-end wrench to free the motor. Then drop the motor down and tilt it, until the top blades of the fan slipHow to Take a Fan Apart out through a wide space in the guard rods. The other blades will then slip up and out toTaking fans apart can be simple, but you free the motor.need the right tools. You need a long, thin FIGURE 50—Small fans will usually have the motor mounted to the rear grill assembly.
58 Electric Heating Appliances and FansIn some older desk fans, the guard is in one The wattage rating of motors is found onpiece and you have to remove the blades first. the nameplate. In many of the small fans,Reach through the wires of the guard and the rating is stamped into the metal base onloosen the setscrew. Slip the blades off the the bottom plate. In larger fans, the rating isshaft. Sometimes the blades will have to be stamped into the end bell of the motor orpried off with a screwdriver. Leave the blades on a small plate riveted to the motor frame.inside the guard. Now the motor-mounting Small fans will have a rating of about 50 wattsnuts can be removed and the motor taken off. on up to perhaps 100 to 150 watts. Large fans can draw high currents, depending on theIn some box-type cased fans, the guard grilles size of the motor.are flat and are held in place by four screwsor molded clips at the corners. If the front In the two-speed and the three-speed motors,and the back guard grilles are taken off, all make the continuity tests in each positionof the inner parts are exposed. This type of of the switch. If the motor runs in thefan is much easier to work on than the round HIGH position but will not run at all in theones. The motor is mounted on two mounts MEDIUM or LOW position, check to seewith bolts or it’s riveted to the case. The type which type of speed control is used. If theof mounting will be visible as soon as you tapped-resistor control is used, this symptomremove the grilles. means that the resistor, or the switch, is open. The motor itself is obviously not faultyTo take the motor itself apart, remove the because it runs in the HIGH position, intwo nuts which hold the two halves of the which the resistor is not used.motor together. Remember to match-markthe cases. Carefully pry the end bell loose, In the multiple-winding motor, failure ofprying first on one side and then the other the motor to run in a given position couldand working the end bell loose until it mean that there is an open circuit in eithercomes off freely. the selector switch or one of the field coils used for that speed. Break the circuit and make continuity tests across the selector switch contacts. Set the switch to the faultyHow to Test the Speed position. Make a quick check by connectingControl small jumpers across the suspected switch contacts. If the motor runs normally withIn the single-speed fan motor, very little the jumpers bypassing the switch, theelectrical testing is required. Only three parts switch is bad.need testing: the line cord, the switch, andthe coils. The coils are connected in series, In the electronic control circuit, if the motorand the continuity test is simple. Connect will not run at all or if the speed control hasthe clips of your digital VOM, set for meas- no effect on the speed, take the control unituring resistance, to the prongs of the line completely out of the circuit. Connect theplug, and turn the fan switch on. Actual circuit by jumpers, without the control unit.resistance readings will vary with the size If the motor now runs at full speed, the controlof the motor. The smaller motors will have a unit is at fault. The unit will normally havehigher resistance than the larger ones because to be replaced. Also, a silicon-controlled recti-they are wound with much smaller wire. fier, or SCR, cannot be easily tested in the shop. The jumper test is the fastest and best test for any of these controls.
Electric Heating Appliances and Fans 59Burned-Out Motor Coils enamel with your fingernail, so that the bare copper will be visible. Pushing on the endsWhen a motor runs normally, it draws the of the coil with your fingertip will make arated amount of current. The energy is “crunch” sound; the whole winding willdissipated in turning the rotor, and the coils be charred.do not get too hot. Practically all small A coil which has been burned from an internalmotors will run cool enough, at approximately short circuit will draw a very heavy current50° C (120° F), so that you can hold your hand because of the large number of shorted turns.on the shell. However, if the rotor is stuck You can determine the current by measuringand cannot turn, the coils will draw a very the resistance of the coil and calculating theheavy current. This current is called the current using Ohm’s Law. However, if youlocked-rotor current, or stall current, and it see a coil burned like the one just described,actually flows through the motor coils at the you have found the trouble, and you don’tinstant the current is applied, before the rotor need to make a current test at all.starts. However, this heavy current normallyflows for only a split second, and won’t do Because of the way small fan motors are built,any harm. it is not possible to rewind them economically. It would cost more to rewind this type of motorIf the rotor is jammed, the heavy current will than it would to buy a new one. Only the verykeep on flowing and the coils will overheat. If large, more expensive motors can be rewoundthe overload is left on long enough, the coils profitably. However, rewinding is a job for awill burn out. The coils are wound with specialist. There are shops which do nothingenamel-coated wire, and if the wire gets hot but motor rewinding and have all the specialenough, the enamel insulation will char or tools and test equipment to do it. Any motorbreak down, and some of the turns of wire smaller than about 1 horsepower (hp) is usuallywill be shorted to each other. In any coil with less costly to replace than to rewind.continuously flowing current, the magneticfield around one turn will induce current toflow in all turns close to it. If any one of theturns is shorted, the turn becomes a continu- Dragging Bearingsous loop. Instead of the current flowing onthrough the coil as it should, it will circulate Except for a blade so badly bent that it hitsaround and around this one turn, getting the guard and locks the motor, only dragginghigher all the time. Every pulse of current bearings can cause a fan motor to burn out.from the line will add more induced current, Dragging, or excess friction, in the bearingsuntil the wire finally burns out. is due to too little oil or damaged bearings. This will cause the motor to pull an extra load andThe overheating affects neighboring turns, run very hot. You won’t be able to holdand they too may become short-circuited. your hand on the motor housing. If theThe end result may be that practically all bearings are allowed to become dry, theyof the wire in the coil is burned and shorted. will sometimes seize, or freeze, tightly toYou can determine whether this has happened the shaft and lock the rotor.by examining the ends of the coils which arevisible when you take one of the end bells Dragging bearings are easy to check. Justoff. The enameled wire should be a fairly dark spin the fan blades with your fingertip.reddish brown and the coating should be (Be sure that the plug has been pulled out.)almost transparent. If it has overheated and The blades should spin very freely and coastburned, it will be completely black. You will for a long time before stopping. If the bladebe able to scrape off small bits of the burned turns only two or three times and then stops
60 Electric Heating Appliances and FansFIGURE 51—The end bells contain the bearings and the oil-filler tubes.very suddenly, the bearings are undoubtedly coils. The oil itself won’t do any damage, but itdragging. Very slow starting and slow run- will invariably cause a heavy accumulationning are other common signs of bearings of dirt, dust, and lint to stick to the inner partsdragging because of lack of oil or damage. of the motor. This will clog up the ventilation holes in the end bell and can even build upSmall fan motors use a caged-ball bearing. to such a thickness that it can get into the gapLarger motors use a sleeve bearing in their in the frame and cause a heavy drag on theheavy end bell. The ball in the caged-ball motor. In actual operation, fan motors needbearing is mounted in a thick felt washer oiling only about once a year, because thewhich serves as an oil reservoir. When the felt will hold quite a bit of oil. When reas-bearing needs lubrication, it will begin to sembling a fan motor, make sure that bothwarm up. If the felt is well saturated with oil holes are on the same side and that theoil, the heat will thin out the oil, and some motor is mounted in the frame with the holesof the oil will run through the oil holes into pointing up. If they point down, the oil willthe inside of the bearing. run out.You can see one of these bearings in the openend bell of the motor in Figure 51. The tinytube going from the cage out through the Worn Bearingsside of the end bell is an oil-filler tube; there When the motor has been taken apart,is another one on the other bearing. The outer examine the rotor shaft at the point whereend of the tube is flared out to form a tiny the oil tubes run in the bearings. The bearingsfunnel. Use an oil can with a very small spout should be very smooth and shiny, like ato feed oil into the funnel one drop at a time. mirror. But if a bearing has run dry for tooKeep applying the oil until it no longer runs long, the friction will have heated up thedown the tube into the felt. When the reser- bearing and the shaft, scoring the shaft orvoir is full, the oil will run over. causing the smooth surface to be gougedDon’t over-oil this type of motor. Excess oil will by bits of metal or dirt. If the shaft is scoredrun down the tube, get onto the rotor, and be badly enough that you can see it, or feel thesprayed onto the end bell, the frame, and the roughness with your fingertip, the motor will have to be replaced.
Electric Heating Appliances and Fans 61Worn bearings become very loose on the shaft, The blade shape and the blade angle areand loose bearings in any electric motor will designed to minimize the blade noise.make the motor rattle very loudly as it runs,even though the rotor spins freely and doesn’t The quietness of a fan depends mostly on thedrag. With a worn bearing, the rotor will vibrate balance of the blades. If the blades are properlyback and forth in the gap. balanced, the fan will not vibrate as it runs. If it does vibrate, you’ll hear quite a bit ofIf the shaft is simply dirty, clean it up with noise, especially with desk fans. The vibrationvery fine sandpaper, re-oil it, and put the of the fan is transmitted through the desk onmotor back together. Test the motor by which the fan is standing, and the noise canrunning it without a load to see if it rattles. be very annoying.You can sometimes tell whether bearings arebadly worn by grasping the shaft in your The blades must have static and dynamicfingers and moving it back and forth. If balance. If the weight of a blade is not evenlyyou can hear a clicking sound, the bearing distributed, the blade does not have staticis too loose. balance and is off center. If the angle of a blade is different from the angle of the restIn larger motors with sleeve bearings, the of the blades, the blade does not havebearings can be replaced if they are worn. dynamic balance. Therefore, it pushes theIn small motors with caged-ball bearings, air either too hard or not hard enough. Anyit is less costly and faster to replace the whole unbalanced condition of the blade causesmotor. Most motor parts are riveted together, vibration and excessive noise.making it very difficult to replace bearingseven if you can get new parts, which is oftenimpossible. How to Tighten a Loose Hub Most mechanical troubles in fans are looseCauses of Noisy Fan parts which cause noise and vibration. OneOperation common cause of rattling and noise, espe- cially in low-priced fans with aluminumOne of the most important requirements of blades, is a loose hub. Check the setscrewa fan is quiet operation. Of course, any loose to be sure that it is firmly tightened on theparts on the blades, the guard, or the motor shaft. If it is, then the hub itself may havewill rattle when the fan is running. So turn come loose from the blades, or, if the bladesthe fan on and listen. If there is a loose part are riveted, a rivet may be loose. You canon the fan, simply tighten it firmly. But if sometimes see the loose parts by examiningthere is no loose part on the fan, the only the blades and the hub closely while holdingpossible sources of noise are the motor and the hub in one hand and moving or tappingthe blades. A normally operating electric the blades, listening for a clicking or rattlingmotor makes only a very low, humming sound, when the fan is off.noise; most fan noise comes from the blades If a rolled-on hub loosens, it will make a loudwhile they are moving rapidly through the noise. There are several ways of remedyingair. Early fan models made quite a loud, this. One way is to take the blades off andrushing sound, especially when they turned put the hub on a smooth surface, such asvery fast. The blades used on modern fans, the back of a vise or a heavy block of metal.however, have been designed to produce A large, round punch, with a flat end largeras little turbulence, or whirling motion of than the hub, can be held over the roll toair, as possible. Many fans have very large keep the roll even, or straight, while tapping.blades which actually overlap each other.
62 Electric Heating Appliances and Fans FIGURE 52—Chisel marks can be seen at the center of this fan hub.Now carefully tap the roll with a light A still better and easier way to hold a loosehammer. This will rivet the roll down hub is to use universal epoxy-resin cement.again and hold the blades. Clean the hub and the blades thoroughly. Then make up a small amount of the cementAnother way to tighten the hub is to use a and run a bead of it on the front of the blades,small cold chisel. Set the chisel blade at right working it well down inside the loose joint.angles to the roll and tap the roll lightly. Do Turn the blades over and apply more cementthis at several equally spaced points around to the back. Be sure that the cement doesn’tthe hub. A rolled-on hub tightened by a chisel run down onto the blades; it is very hard tois shown in Figure 52. The four cross marks remove once it has set. Place the blades flatindicate the points where the chisel crushed and let the cement dry overnight. Also, makethe rim. sure that none of the cement drips into theIf the hub and the blades are not made of shaft hole in the hub.aluminum but of some other metal, you cansometimes solder them together. Remove alloil and grease and scrape the surfaces as clean How to Check Blade Anglesas possible. Use a heavy soldering iron orpropane torch. The large area of the blades Fans are made with either three or fourwill conduct the heat away from the hub very blades. Most small fans are of the four-bladequickly, making it hard to get enough heat for type. In all types, however, the angle of eacha good solder joint. Do not leave blobs of blade to the center line of the shaft must besolder on the outside, because they may exactly the same. The blade angle in Figure 53unbalance the hub. Make as smooth a joint is about 80 degrees. If the angle is not theas possible. same for all blades, the blades are dynami- cally unbalanced. If you detect an unusual
Electric Heating Appliances and Fans 63vibration or noise and nothing seems to beloose, check the blades to see if one is bent POSITION OFout of line with the rest. TESTED BLADEA blade-angle check cannot be made visually; TIP-CHECKER FAN ARMa simple blade-angle checker should be used. MOTOR WIREYou can make such a checker from a coupleof pieces of sheet metal or heavy cardboard, WING NUTas shown in Figure 54(a). The piece that serves BOLTas a base should be heavy enough to hold FAN BASEthe arm. The two parts are held together by ANGLE BASEa small bolt, a couple of flat washers, and a CHECKERwing nut. The wing nut is loosened justenough to allow the arm to be set; then thewing nut is tightened to hold the arm.The angle checker is shown in use in 54(b).The fan is left on its base and the guard isremoved. Set the checker on the bench infront of the fan and slide the arm into contactwith any one of the blades. It is helpful tonumber the blades 1, 2, 3, and 4 with a softpencil for reference. Now, lock the arm sothat it cannot slip. The arm should touchthe blade at front and back edges. Mostblades are flat-surfaced, but even if theblade is curved, you can set the arm sothat it touches the front and back edges. BLADE FIGURE 54—A blade angle checker (a) can be constructed of sheet metal or heavy cardboard. CENTER LINE HUB OF SHAFT Now, turn the blades, checking the angle of each blade. If any blade does not touch the ANGLE BETWEEN arm, carefully bend that blade until it has BLADE AND SHAFT the same angle as the others. You can bend CENTER LINE the blade with your fingers, because the blades are made of thin sheet metal. END VIEW OF BLADE BLADEFIGURE 53—The angle of the blades must be thesame to prevent excess noise.
64 Electric Heating Appliances and FansAdjusting Blade Tips For a final test, set the fan on the bench, with the guard off to eliminate a possible cause ofYou can make a tip checker by attaching noise. Turn the fan on, but make sure that thea loop of stiff wire to the other end of the blades cannot hit anything. If the blades areangle-checker base that is shown in Figure 54. well balanced, they will run very smoothlyMake a right-angle bend near the tip end of and quietly. Replace the guard and recheck.a wire and tightly bolt the other end of the Any noise you hear now must be due to awire to the base. Set the fan upright on the loose part in the guard itself.bench and place the tip of the wire underthe bottom blade so that it just touches theend of the blade, as shown in Figure 55. Loose Parts on GuardsTurn the blades slowly, and observe the blade If metal rods make up the guard they cantips from a position at right angles to the cause noise which is sometimes hard to locate.motor shaft. All blade tips should be exactly The rods should be spot-welded together atin line fore and aft. If any blade tip is out of the points where they cross each other, to pre-line, bend it until it is aligned with the other vent any noise. These small welds, however,blade tips. If a blade is out of line, the blade may break from rough handling or droppingtips will not travel the same path through of the fan. To locate the sources of the noise,the air and will cause more air turbulence run the fan at all speeds and listen. Sometimeswhen the fan is running. The bent blade will you will find that a guard will rattle at one“whip” as it runs, and the fan will vibrate speed and not at another.badly. In this test, do not change the angle ofthe blades; just bend the blades forward or Examine the guard very carefully for anybackward. broken welds or loose rods. If you can see any, run the fan, and listen. Hold the guard rods together at suspected points and see if the noise stops. Be careful not to put your fingertips inside the guard; the rapidly 1 PATH OF spinning blades can give you a painful cut. MOTOR BLADE TIPS If you find a loose joint or weld, you can 4 POSSIBLE usually repair it with a dab of epoxy-resin 2 POSITIONS cement. Clamp the loose rods together after OF BENT TIP placing a small drop of this cement between 3 ARM them. Let the cement set, and the trouble TIP-CHECKER will be remedied. WIRE Guard rattle in metal box-type fans is often BOLT BASE due to broken welds in the case. Examine the case carefully around the joint where the ends of the metal are welded together. Loose motor- mount rods or loose screws which hold the guard to the case are other common sourcesFIGURE 55—A tip checker can be used to check of trouble.the fan blade for bent tips. You can also lay theblade on a flat surface. In practically all fans, you will find self- tapping screws. If a screw has been taken out and replaced several times, the hole may be worn until it is too big to allow the screw
Electric Heating Appliances and Fans 65to be tightened firmly. This is also a source be replaced. If a fan does not have feet, theyof noise. If you can reach to the back of the can be added; or, long strips of foam rubberhole, you can replace the self-tapping screw or thick felt can be cemented to the base towith a machine screw, a flat washer, and a provide insulation against noise.nut. Use a lock washer under the nut; thevibration of a fan can make a bolt and nutwork loose in a surprisingly short time. Oscillating FansIf you are not able to stop the noise aftermaking all the suggested repairs, take the Many fans have an oscillating mechanism.guard completely off, and put small rubber A small gearbox on the back of the motorwashers under each of the mounting screws makes the fan turn slowly from side to sidebetween the guard and the case. This will to spread the stream of air over a wider area.help reduce the undetermined noise. The The fan is adjustable; it can be locked so thatmotor can also be mounted on small rubber it stands still, set halfway for a small amountgrommets or washers to cut down the noise. of movement, or all the way for the full sweep of oscillation. An exploded view ofMost fans have rubber feet to reduce the an oscillating fan is shown in Figure 56.noise and the transmission of vibration. Ifthese feet are old and hardened, they can MOTOR MOTOR COVER AND GEAR NUT REAR GUARD LOCK SCREW ASSEMBLY BLADE WASHER GUARD MOTOR REAR POWER MOTOR COVER CORD OSCILLATOR ESCUTCHEON SWIVEL ASSEMBLY HOUSING LINE CORD SCREW BASE TILT-ADJUSTING SCREW MOTOR STRAIN RELIEF DETAILS KNOB SECONDARY OSCILLATING CORD NUT GEAR LOCK WASHER LID SCREW BRACKET SWITCH BRACKET WASHER GEAR TRAIN FOOT BOLT ASSEMBLY STATOR SCREW RESISTOR ROTOR AND SHAFT ASSEMBLY SHAFT AND CRANK ASSEMBLYFIGURE 56—The component parts of an oscillating fan are shown in these exploded views. (Courtesy of Westing-house Electric Corp.)
66 Electric Heating Appliances and Fans PIVOT ATTACHED TO FAN BASE AND STANDS STILL ECCENTRIC ARM TURNS LINK THIS WAY DIRECTION OF FAN ECCENTRIC ARM PISTON-GEAR SHAFT, ATTACHED TO MOTOR (a) LINK ARM AN OFF N (b) C TIO D IRE ARM DIRECTION OF FAN LINK (c) DI RE CT IO N OF FA N LINK ARM (d)FIGURE 57—The four phases of an oscillating fan’s movement are shown here.Let’s see how oscillation is obtained. The fan In 57(a), the eccentric arm is turned all themotor is mounted on a pivot so that it can way to the left. The link has pulled the fanturn freely from side to side. The back end motor to a position where the fan is blowingof the motor shaft is cut into a worm-gear straight forward. As the shaft turns, the armshape which drives a pinion gear. The pinion turns clockwise. At 57(b), the arm has turnedgear turns at a much slower speed than the all the way to the front. The back end of themotor shaft, or at about ten revolutions per motor has been pulled to the right, so thatminute. The pinion-gear shaft drives an the fan is now blowing to the left. At 57(c), theeccentric arm, and the end of this arm is arm is all the way to the right. This pulls theattached to a link. The other end of the link back end of the motor to a straight positionis attached to the fan base, which stands still. so that the fan blows straight forward. At 57(d),As the eccentric arm is moved, the motor is the arm is all the way to the back. This pullspushed all the way to one side, then pulled the back end of the motor to the left, so thatback and pushed all the way to the other side, the fan blows to the right.to give the fan its oscillating motion. A fullcycle of oscillation is shown in Figure 57.
Electric Heating Appliances and Fans 67FIGURE 58—In this fan, a gearbox is used with an eccentric arm to create oscillating motion.In actual oscillating fans, the eccentric arm Repairing Combinationhas a U-shape, as shown in Figure 58. It ismade this way for two reasons. The U-shape Light/Fan/Heatersallows the actual pivot point to be directly Combination light/fan/heaters are usuallyunder the end of the pinion-gear shaft which installed in the ceiling of a bathroom.drives the eccentric arm. The slot allows the Their purpose is to provide a ceiling light,hollow locking nut to be slipped back and exhaust fan, and heater for the bathroom.forth to adjust the amount of oscillation. An exploded diagram of a typical assemblyWhen the nut is set directly under the shaft, is shown in Figure 59.the eccentric arm has no effect and themotor stands still. When it is set to the far The customer’s complaint for this type ofend of the eccentric arm, the fan travels its unit can include total failure of operation,farthest distance while oscillating and has the loss of one section, or excess noise ora maximum swing. The locknut can be set vibration.halfway or at any other point to get theamount of swing desired. Total failure of the entire unit is most likely caused by the loss of the AC power serviceThe oscillating gear arrangement rarely causes to the unit. This could be caused by a typicalany trouble. If the link and the eccentric arm circuit breaker or blown fuse, open wire, orrun dry of oil, it could cause a drag on the loose connection. The first place to check ismotor. However, this is very easy to remedy. at the circuit breaker or fuse box. These unitsJust loosen, clean, and reoil the link and the require one dedicated service of 20 amps.eccentric arm. These parts should be lubricated If the circuit breaker or fuse is in proper order,with a cream grease so that it will not drip off the next location to check is at the switchthe back of the fan onto the desk or floor. assembly for the unit. In these systems, one common AC hot line (black) is tied to three
68 Electric Heating Appliances and Fansswitches in one wall mount box. You should failed. The second possibility is that the sec-measure 120 VAC between the black wire tion of the unit itself has failed.and the ground or the white (neutral) wire.Failure to measure 120 VAC would mean a Notice the use of standard plug-type recep-problem in the residential service. If 120 VAC tacles with the unit. Once the grille has beenis present, the problem is most likely on a removed, the sections can be easily seen andconnection to the switches. serviced. Pull the plug from the receptacle for the failed section and check for the presence ofThe failure of only one section of the 120 VAC at the receptacle. If 120 VAC is notcombination unit could be caused by two present, you should check for a loose jumperpossibilities. The first possibility is that the or failed switch at the switch box. If 120 VACblack jumper between the switches has is present, the section can be removed from the housing for closer inspection. GROUND (GREEN OR BARE WIRE) 2 1 NOTCH 3 32 GROUNDING CLIP GROUNDING 31 DETAIL 4 5 6 9 7 30 8 28 11 28 9 26 12 27 13 10 14 25 22 16 15 20 19 29 26 23 22 16 23 24 11 18 17FIGURE 59—An exploded view of a combination heat/light/fan is shown here. (Courtesy of Nautilus)See page 84 for key to parts.
Electric Heating Appliances and Fans 69The only unusual component of the combi- (28). The other filters in this unit are the deo-nation unit is in the heater section. Here, a dorant filter (11) and a metal mesh filter (12).device known as a thermolink is used (item 20in Figure 59). This link is used to disconnect The fan assembly uses a shaded-pole motorthe heating element in the event of a short (45) and a squirrel-cage dual blower (47).circuit in the element or fan failure. If the The only other electric components are twotemperature within the housing gets too great, switches (39 and 55) and the pilot lightthe thermolink will open, opening the circuit. assembly (19). Switch 39 is the power ON/OFFIf you need to replace the thermolink, use switch which disconnects power from thean exact replacement from the manufacturer. high-voltage transformer in the event theAlso, make sure to look for the original cause case is opened.of failure of the link. The unit may requirefurther repair such as heating elementreplacement or fan motor replacement. Servicing Air Purifiers The most common failure of electrostatic air purifiers is due to the collection of dirt on theAir Purifiers filters, screens, or plates of the appliance.One special type of fan unit is the air purifier Usually this dirt, which is slightly conductive,shown in exploded view in Figure 60. This will even attach itself to the insulators whichtype of appliance is used to remove dust, hair, support the plates, or screens. The dirt willpollen, and odors from the household air. then conduct the charges away from the plates or screens, limiting the purifier’sMost electric air purifiers operate on the operation. Usually a snapping or poppingprinciple of electrostatic precipitation. Here, the sound will be heard within the appliance.air passes through metal plates, or screens. The remedy is to simply clean all electro-One plate, or screen, is charged with a high static component parts, and to replace thenegative voltage. This action causes the dust charcoal and mesh filter elements.and dirt particles to also be charged as theypass near the plate, or screen. The air with the Electrically, the troubleshooting of an aircharged particles then passes through a posi- purifier is similar to the troubleshooting oftively charged plate, or screen. Since unlike other appliances. The line cord and powercharges attract, the charged particles will ON/OFF switch should be checked usingbe attracted to the plate, or screen, and the continuity tests covered earlier. How-removed or precipitated from the air. ever, these items can be visually checked by looking at the pilot light with the unitNormally, air purifiers such as this one will plugged in and the switch turned ON.contain a charcoal filter which will removeodors and a mesh paper, or metal filter, which The transformer and rectifier assemblywill remove larger dirt particles ahead of the can also be tested with a digital VOM.electrostatic screens, or plates. The primary resistors of the transformer will be fairly low, typically 10 to 20 ohms. TheThe power supply for this unit is item 52 secondary side of the transformer that con-(Figure 60), which is a high-voltage transformer nects to the plates will display a very highand rectifier. Since high-voltage is used, it is resistance. This resistance will normally beespecially important to remove power before above 2K ohms (two thousand ohms). If aservicing. The high-voltage transformer is high-voltage rectifier is used, the resistanceconnected to the plates (26) and an electrode reading in one direction may read an open(27). The plates are held apart by insulators circuit. If this type of reading occurs, the test
70 Electric Heating Appliances and Fans 1 2 3 10 11 12 4 13 5 6 17 6 68 8 22 19 18 20 23 24 25 26 27 32 36 28 26 28 41 51 45 46 33 47 52 38 9 39 49 65 50 60 54 55 61 62 64 67 63FIGURE 60—The component parts of an air purifier are shown here. (Courtesy of Sunbeam Corporation [Canada]Limited)See page 71 for key to parts.
Electric Heating Appliances and Fans 71leads should be swapped and a second The final items to check on this appliancemeasurement taken through the transformer are the operation of the safety switch andsecondary and rectifier. Certain high-voltage the fan assembly. The safety switch can berectifiers display a very high forward biased tested for continuity with the power removedresistance, causing the forward resistance from the appliance. When the switch lever ismeasurement to be very high, up to 5M depressed, the resistance across the switch’sohms (five million ohms) through the rectifier contacts should be near zero ohms. Whenand transformer. Because of the high voltages released, the switch should show near infinityinvolved, do not measure the voltage output or ohms or an open circuit.the voltage on the plates, or screen, withoutusing a high-voltage probe. The fan system should be tested as seen earlier in this section. KEY FOR PARTS IN FIGURE 60 1 GRAY COVER 32 CORD ASSEMBLY 2 ORNAMENT 36 POWER CORD COMPLETE 3 UPPER CASE GRAY 38 SWITCH RETAINER 4 LOCK BUTTON 39 SWITCH 5 LOCK PLATE 41 MOTOR CUSHION (4) 6 HELICAL SPRING 45 MOTOR ASSEMBLY 8 SUPPORT PIECE 46 HELICAL SPRING 10 FILTER FRAME 47 FAN COMPLETE 11 DEODORANT FILTER 49 OILLESS BEARING-BRASS 12 METAL FILTER 50 BEARING HOLD 13 FILTER FRAME A 51 INSULATOR ASSEMBLY 17 GUARD NET 52 HIGH TENSION UNIT 18 LAMP COVER GRAY 54 SWITCH INSULATOR 19 PILOT LIGHT 55 SWITCH 20 LEAF SPRING 60 SWITCH BRACKET 22 LOWER BLACK 61 HELICAL SPRING 23 LAMP INDICATING PANEL 62 SWITCH LEVER 24 LOWER ORNAMENT 63 EARTH PLATE 25 SEALER (5) 64 NAME PLATE 26 ELECTRODE (2) 65 LOWER CASE GRAY 27 DISCHARGE WIRE ASSEMBLY 67 STAND PIECE 28 INSULATOR A (2) 68 COLLECTING SHOE
72 Electric Heating Appliances and Fans ✔ Check It Out! 6 1. What is an oscillating fan? _________________________________________________________________________ 2. How can a fan be made to pull the air into a room instead of exhausting it? _________________________________________________________________________ 3. What is the advantage of an induction motor over a shaded-pole motor when used in a fan? _________________________________________________________________________ 4. What type of fan is the easiest to take apart? _________________________________________________________________________ 5. How would you know that the coils of a fan motor have burned out? _________________________________________________________________________ 6. How would you repair dragging bearings? _________________________________________________________________________ 7. What is the cause of noisy blade operation in a fan? _________________________________________________________________________ 8. How can the dynamic unbalance of blades be determined? _________________________________________________________________________ Check your answers with those on page 83.
Electric Heating Appliances and Fans 73ATTIC FANS AND POWER Types of Fans andVENTILATORS Ventilators There are many types of attic fans. One typeBecause heated air will rise above cooler is the gable fan which is mounted in the gableair, attic temperatures in the summer months of a home. If the homeowner has a removablecan be extremely hot. Also, shingled roofs ceiling panel in the attic, the fan will pull airof any color which are in the direct sun can from the home’s living area to be exhaustedradiate quite a large amount of heat into the through the attic. If no removable panel isattic space of a home. present, a second vent is normally provided in the opposite gable of the home. The outsideAttic heat will add an extra burden to an air is pulled in through the gable vent and theair- conditioned home. The easiest method hot attic air is exhausted through the gableof removing this heat is by using a powered fan. A typical gable fan is shown in Figure 62.attic fan or ventilator. Figure 61 shows howan attic fan can be used to pull cooler air from A second type of powered ventilator is shownthe outside of the house through the attic. in Figure 63. This type of fan is mountedThe heated attic air is exhausted, resulting directly to the roof of the home. As with thein a cooler home. gable fan, fresh air can enter the attic space through a removable ceiling panel or through gable vents.FIGURE 61—With the help of a powered attic fan, heated air is allowed to escape from the attic to allow fora cooler home. (Courtesy of Nautilus)
74 Electric Heating Appliances and FansFIGURE 62—A gable fan is mounted in the upper FIGURE 63—A powered ventilator mounts directlygable portion of a home. (Photo Courtesy of Nautilus) to the roof between the roof rafters. (Photo Courtesy of Nautilus)The normal supply power for an attic fanor powered ventilator is standard 120 VAC. If possible, open the circuit breaker box orThe supply power is applied to a thermostat fuse box and verify that this voltage is actuallywhich is used to control the fan’s motor. In passing through the circuit breaker or fuse.this manner, the fan will turn on when the A rare, but possible occurrence is that a circuitattic space reaches a certain temperature and breaker will fail internally or a fuse holderturn off when the temperature is reduced. will not make proper contact and not pass the AC power to the circuit. It is also possible that the neutral (white) wire can shake loose of the neutral bus in the box. In this case, theServicing Attic Fans and hot side of the power will be delivered toPower Ventilators the fan, but with no neutral the circuit will be open.The troubleshooting of an attic fan, or powerventilator, is similar to the troubleshooting If power is being provided at the service,and repair of most other types of fans. The the next place to check for AC power is atexception is that a thermostat is present in the thermostat in the attic. The thermostat isthe power circuit. easily located by following the service cable as it leads to the fan assembly.Checking the Power Supply Taking a measurement at the thermostat should also reveal approximately 120 VAC.The first test to make on this type of system is If 120 VAC is present, the trouble can beusually at the circuit breaker or fuse box in the found at the thermostat or motor. If 120home. One fuse or circuit breaker should be VAC is not present, the problem is in thededicated solely to the attic fan or ventilator. electrical service to the system.Check to see if the circuit breaker is trippedor the fuse is blown first. This action can save In some older homes, you might find thatyou from climbing into a high-temperature the power for the fan was inadvertentlyattic space. tapped from an attic lighting system. In this case, follow the service back and measureAs previously mentioned, all attic fans, or the voltage at the location of the tap. Often,ventilators, normally operate on 120 VAC. you may find a switch box is the location of the tap. Here, you will probably find that
Electric Heating Appliances and Fans 75the wiring has become loose and either Also, make a note of the temperature settingthe hot (black) or neutral (white) wire has of the original thermostat and match thisbecome disconnected. You should, therefore, setting on the replacement thermostat. Andisconnect power at the circuit breaker or exact replacement thermostat is not normallyfuse box and make the proper connection. required in this situation. However, the contact ratings must be equal to or larger than the original thermostat to prevent earlyTesting the Thermostat failure. Standard home thermostats for theThere are two types of thermostats used control of home heating systems should notin attic fans or ventilators. These types are be used since their contacts are low-voltage,the single-pole single-throw, and double- low-current contacts which will be quicklypole single-throw types. The action of the destroyed by the high starting current of thethermostat remains the same: opening and motor.closing the circuit depending upon the airtemperature. Most attic thermostats are Checking the Motoradjustable and will close the circuit to thefan motor in the range of temperature from The motor of a whole-house fan can be21° C to 55° C (70° to 130° F). Double-pole checked in three different ways. First you canthermostats offer the advantage of opening check the motor for visible signs of failureboth sides of the AC power line when the such as burn marks, and use your sense ofthermostat opens. smell to check for the odor of burnt insula- tion. The next test is a mechanical check ofThe testing of a thermostat is relatively the motor. Here, you would spin the fansimple. In a single-pole thermostat, you blades and check for dragging bearings orcan perform a voltage test at the line and mechanical interference of a fan blade tothe load side if the neutral wire is accessible. the housing. Remember, it is important toHere you set the meter to read AC volts and remove power before performing these tests.attach one lead of the meter to the neutral(white) wire. Next, you test the voltage using The third test is an electrical test of the motor.the other test lead at the line and the load leads Most motors will have a resistance in the rangeof the thermostat. If the air temperature is of 10 to 30 ohms, depending upon the size ofhigh enough to cause the thermostat to close, the motor. A resistance less than 10 ohms isyou should measure 120 VAC at both of the very suspect and is the most likely cause ofterminals. If the line side is missing, there repeated blown fuses or tripped circuit breakers.is a problem in the electric service as pre- For example, a resistance of 6 ohms wouldviously covered. If the thermostat should cause a current draw of 20 amps. This is thebe closed and the voltage is not present at maximum rating of most residential branchthe load side, the thermostat has failed and circuits except for ranges, water heaters, andshould be replaced. well pumps, which can be as high as 50 amp circuits. Even at 10 ohms, the motor will drawIn replacing a thermostat, make sure to 12 amps of current, which is possible only onremove AC power from the circuit at the some large fan units.fuse or circuit breaker box. Do not simplyswitch off the power at an attic switch, if As with low resistance readings, high resis-present, since someone may have uninten- tance readings on a motor are also suspect.tionally switched the neutral instead of the If you read a resistance above 30 ohms, thehot side of the service. motor may contain an open field coil or open centrifugal switch. In either case, the motor will require disassembly and inspection as
76 Electric Heating Appliances and Fans 18 THREE BLADE FAN 19 FOUR BLADE FAN 15 CAPACITOR START MOTOR 3 THERMAL PROTECTOR 16 MOTOR MOUNTING BOLT 12 CAPACITOR 14 RETAINING SCREW 13 CAPACITOR MOUNTING BRACKET 11 MOUNTING BAR RETAINER (1) 9 MOTOR MOUNTING BAR 17 RETAINING NUT 20 HOUSING CLAMPING 10 MOUNTING BAR BOLT (4) RETAINERS (2) 8 HOUSING 7 THERMOSTAT 21 FLAT WASHERS 8 THERMOSTAT BRACKET 22 SELF-LOCKING NUTS (4) 5 THERMOSTAT BRACKET SCREW 1 SHUTTERS 4 MOUNTING SCREWS (4) 2 SHUTTER STOPFIGURE 64—This exploded diagram reveals the components of a gable fan. (Courtesy of Nautilus)
Electric Heating Appliances and Fans 77covered earlier under split-phase and capaci- each of the three fan blades. Once centered,tor-start motor operation, trouble-shooting, the housing can be tightened by means ofand repair. Normally, if a field coil is damaged, the four bolts that clamp it to the woodenyou should replace the motor. Remember that stud. To make sure the bolts don’t loosen,a shorted squirrel-cage rotor winding or use lockwashers, self-locking nuts, or use afaulty capacitor can also cause problems liquid locking agent on the threads of eachsuch as overheating and failure to turn. This bolt before the nut is tightened.type of failure can also cause vibration tooccur if the motor does start turning. The motor mounting bar (9) can also work free during service. This bar is simply nailed or screwed into the vertical studs and boltedMechanical Repair and to the motor. If the bar was nailed and hasAdjustments worked loose, replace the nails with screws. Also, check the tightness of the motorToday’s products are engineered and mounting bolts as part of your inspectionconstructed in such a manner as to provide and repair procedure.many years of trouble-free service. However,failures do occur and these failures are usually The final item to check on this assembly wouldcaused by faulty installation of the fan or be the fan blade assembly. As shown earlierventilator. in this text, inspect the tightness of the hub on the motor shaft, rivets on the blade arms, andMost of the customer complaints that you will fan blade angles. One method of checking theexperience are either total failure or excess angles on such a fan is to remove the hub andvibration or noise from the fan or ventilator. fan assembly from the housing and lay itTotal failure will normally occur due to failure on a flat surface. All three or four bladesof electric service, thermostat, or a motor, should touch the surfaces evenly. If one bladewhich were covered earlier. This section will appears off, gently bend the blade until itdeal with the second type of complaint, excess is in line with the others.noise or vibration. An exploded view of a roof-mounted powerAn exploded view of a gable fan is shown ventilator is shown in Figure 65. Since thisin Figure 64. If this unit is making excessive ventilator is mounted directly to the roof andnoise or vibration, it will normally be caused partly under the shingles, it is somewhat moreby one of the components becoming loose difficult to service. Vibration or noise can bein service. The easiest method of finding the caused by a loose bracket (6), mount (5), fannoise or vibration is by checking the tightness and hub (3), or cover (2). The easiest itemsof all fasteners in the assembly. Caution: to check are the motor mounting bracket (6),Make sure power is removed from the fan motor (4), and fan (3). These items can bebefore taking these tests. checked from inside the attic space. A loose mount or cover will require a trip to the roof.The shutters (1) should be free to open and Since the mount is under the shingles, it canclose, but should not be loose enough to be difficult to tighten. If this problem occurs,rattle or shake. Worn pivot points for the you can gently pry up the shingles and installshutters is cause for replacement of the new mounting screws or special serratedshutter assembly. nails. Replace the shingles by applying a liberal amount of quality roofing cementThe housing (8) can also loosen from its under the sealing tabs on the shingles.position and begin touching the ends of theblades of the fan. The housing should becentered by measurement of the housing to
78 Electric Heating Appliances and Fans 1 KEY FOR PARTS IN FIGURE 65 1 COVER SCREWS (3) 2 COVER ASSEMBLY 2 3 FAN AND HUB 4 MOTOR 5 ROOF MOUNT 6 MOTOR MOUNTING BRACKET 7 RETAINING BOLT 3 8 RETAINING NUT 9 MOUNT BOLTS (3) 10 RETAINING SCREWS 4 11 THERMOSTAT MOUNTING BOX 12 BOX RETAINING SCREW 13 THERMOSTAT 14 WIRE WITH PUSH-ON CONNECTOR 15 INSULATOR 5 16 COVER 6 8 7 11 10 9 12 13 14 10 15 10 16FIGURE 65—These are the components of a typi-cal power ventilator. (Courtesy of Nautilus)
Electric Heating Appliances and Fans 79 ✔ Check It Out! 7 1. What voltage is commonly used to power an attic fan or power ventilator? ________________________________________________________________________ 2. What types of motors are usually used with an attic fan? ________________________________________________________________________ 3. Where is the power for an attic fan sometimes tapped from? ________________________________________________________________________ 4. List the common causes of excess noise or vibration from a power ventilator. ________________________________________________________________________ 5. What is the typical range of adjustment for the thermostat in an attic fan or power ventilator? ________________________________________________________________________ Check your answers with those on page 83.
80 Electric Heating Appliances and Fans NOTES
81 Check It Out! Answers 1 14. Wrap the wire clockwise to make a good connection. 1. Defective line cord 15. A grommet protects the line cord at the point where the cord enters the 2. Defective insulation causes a short appliance case. circuit and shock. 16. Broken strands in the cord may make 3. Wire designated AWG No. 16 is a wire contact in some positions and not in of a certain cross section according to others. American wire gage established standards. 17. Two layers of tape are sufficient for covering a splice. 4. Ampacity means the current-carrying capacity of an electric wire. 18. Wire nuts are solderless connectors of wires. 5. Wire AWG No. 12 is larger and carries more current than wire AWG No. 14. 19. Crimp-on lugs are lugs with sleeves The higher the gage number, the which are crimped to the bare wire smaller the wire. to make a terminal. 6. Too small a wire causes overheating. 7. Heater cord uses fiber glass insulation. 2 8. A three-wire cord is needed to ground 1. The thermostat blade is bent when the appliance and protect the user from heated, opening the circuit and stopping shock. the current when the heater is too hot. 9. Grounding wire in a cord is connected 2. A bimetal blade is made of two different to a metal part (usually the case or the metals which expand at different rates frame of the appliance) and through and make the blade bend when heated. the round prong to the ground on the AC line. 3. The most probable cause is an open circuit in a part of the heater circuit.10. Polarized outlets have three terminals, one of which is D-shaped and usually 4. The line cord should have wires which marked “ground.” will carry at least 15 amp.11. A knot in the two wires inside the plug 5. Insulators for mounting heating elements relieves strain on the wire. must be made of ceramic material or mica which can withstand high heat.12. Stranded wires provide greater flexibility Rubber and plastic cannot be used. without breaking.13. The next larger size (smaller gage number) should be selected.
82 Check It Out! Answers 6. Connections on heating elements must 3. The thermostat is attached to the be clean and tight. See method illustrated soleplate. in Figure 18. 4. An electric iron has only one circuit, with 7. The heating coil should be stretched to a heating element and a thermostat con- fit tightly in order to avoid touching the nected in series. metal case. 5. The line cord is permanently attached to 8. After the heater has been repaired, you the iron. An appliance plug is not used. should check it for grounds or leakage. 6. In a cold iron, the thermostat blade is 9. A check for grounds is made with a straight. digital multimeter between a metal part and a grounded object. 7. The vent pipe conducts the steam from the water tank. 8. The ball is lifted by pressure from below 3 and opens the valve. When the pressure is from above, the ball closes the valve. 1. The current would be I = E/R = 120/50 9. The thermostat must fit exactly on its = 2.4 amp. mounting place, such as a bracket, and 2. In order to determine the wattage, you the temperature must match the calibra- should first find the current, or I = E/R tion on the knob. = 120/20 = 6 amp. 10. Ball and flap valves The power is then P = E × I = 120 × 6 = 720 watts. 5 3. The current is I = P/E = 500/120 = 4.16 amp. 1. Because the line cord is moved and 4. The wattage will be reduced one-half. bent in using the iron, it breaks most frequently near the end. 5. a) In parallel, the wattage will be double, or 1000 watts. 2. Remove the cover plate on the handle to expose the terminals. b) In series, the wattage will be 250. 3. Push-on connectors are easier to handle during tests than are screws. 4 4. Any resistance reading across thermostat contacts indicates that the contacts do 1. The heating element is built into a thick not make proper contact, due to dirt or metal soleplate. to burned spots. 2. A steam iron is built the same way as a 5. Scale caused by hard water accumulates dry iron, but it has, in additon, a water in the tubing and holes. tank and steam pipes.
Check It Out! Answers 83 6 7 1. An oscillating fan turns from side to side 1. 120 VAC as the blades spin. 2. Split-phase or capacitor-start motors 2. By reversing the rotation of the motor 3. The attic lighting circuit 3. An induction motor produces more power, which is needed to move the 4. Loose motor mount, motor, housing, fan heavy blades of a large fan. or hub, and roof cap 4. The box type 5. 21° to 55° C (70° to 131° F) 5. The enamel insulation on the coil end is black and can be scraped off with your fingernails. 6. Since the bearings are probably dry, oil them. 7. Static or dynamic unbalance of blades causes noisy operation. 8. Use an angle checker to find out whether all blades make the same angle with the shaft.
84 4 GRILLE SPRING (MODELS 670, 671) (2 REQ’D)KEY FOR PARTS IN FIGURE 40 5 MOTOR 1 ESCUTCHEON 6 MOTOR PLATE 2 SADDLE (ESCT. NOT ENCL.) 7 BLOWER WHEEL (MODELS 670, 671)2A ASSEMBLY SADDLE 8 BLOWER WHEEL (MODELS 688, 689) 3 ASSEMBLY FILL COVER 9 NUT #6-32 (2 REQ’D) 4 COVER & EXCT. REAR 10 DAMPER/DUCT CONNECTOR 5 SCREW REAR COVER 11 RECEPTACLE 6 LENS 12 WIRING COVER 7 ASSEMBLY CORD W/INSERT 13 GROUND CLIP INCLUDES 7A, B, AND C 14 HOUSING ASSEMBLY7A INSERT BOOT KEY FOR PARTS IN FIGURE 597B BOOT CORD7C CORD 1 HOUSING 8 ASSY. HANDLE W/FILL COVER 2 DAMPER 9 KNOB TEMPERATURE 3 MOUNTING BRACKET (4)10 LEVER STEAM 4 RECEPTACLE, WHITE11 PINION DRIVE 5 RECEPTACLE, BLACK12 LEVER TEMPERATURE 6 RECEPTACLE, RED13 ASSEMBLY P.C. BOARD 7 PLASTIC BLOWER WHEEL14 NUT WIRE (2 REQ’D) 8 FAN MOTOR15 WIRE LEAD 9 MOTOR PLATE/PARTITION ASSEMBLY16 CLIP P.C. BOARD 10 NUT (4)17 COUPLING UNIVERSAL 11 GRILLE18 ADAPTOR STAT. 12 LIGHT REFLECTOR19 CONTROL VALVE 13 NUT20 GASKET VALVE 14 LIGHT SOCKET21 TUBE VALVE DRIP 15 LIGHT LENS22 SKIRT (WHITE) 16 BOLT ASSEMBLY23 SCREW BRACKET (3 REQ’D) 17 LOGO BUTTON24 BRACKET REAR (2 REQ’D) 18 GRILLE SCREW25 SCREW THERMOSTAT 10 BLOWER WHEEL26 TERMINAL 20 THERMOLINK27 THERMOSTAT 21 #10-32 NUT (7)28 SCREW BIMETAL 22 HEATER HOOKS (5)29 BIMETAL THERMOSTAT 23 #8 X 1/4 SHEET METAL SCREWS (4)30 BRACKET FRONT 24 HEATER SCROLL COVER31 HEATER THERMAL 25 HEATER SCROLL HOUSING32 FUSE THERMAL 26 HEATER MOTOR33 ASSEMBLY SOLEPLATE 27 #8 X 3/8 SHEET METAL SCREW 28 GRILLE STUDKEY FOR PARTS IN FIGURE 43 29 HEATER ELEMENT 1 GRILLE ONLY (MODELS 688, 689) 30 TINNERMAN NUT #10-32 (2) 2 GRILLE SPRING (MODELS 688, 689) (2 REQ’D) 31 ALUMINUM RECEPTACLE PLUG 3 GRILLE ONLY (MODELS 670, 671) 32 GROUNDING CLIP
Examination 85 EXAMINATION 93041 Electric Heating Appliances and Fans Whichever testing option you choose for your answers, you must use this EXAMINATION NUMBER: 93041When you feel confident that you have mastered the material in this study unit, complete the fol-lowing examination. Then submit only your answers to school headquarters for grading, usingone of the examination answer options described in your first shipment. Send your answers forthis examination as soon as you complete it. Do not wait until another examination is ready.Questions 1–25: Select the one best answer to each question. 1. In selecting the wire size for a line cord, you should remember that A. No. 16 is larger than No. 12. C. No. 8 is smaller than No. 10. B. No. 14 carries more current than No. 18. D. No. 4 carries less current than No. 6. 2. Which one of the following appliance parts gets the hardest service? A. Switch C. Heating element B. Thermostat D. Line cord 3. The color used for the hot side of house wiring is A. green. C. gray. B. white. D. black.
86 Examination 4. An AWG No. 16 line cord with type HPN insulation has an ampacity of A. 12 amp. C. 15 amp. B. 13 amp. D. 17 amp. 5. To heat a room quickly, some electric room heaters are provided with A. a heavy metal case. C. a push-button switch. B. a motor-driven fan. D. an automatic thermostat. 6. If the current flowing through an electric heater increases from 6 to 12 amp while the voltage remains the same, the heat produced by the heater will be A. reduced one-half. C. two times the original heat. B. unchanged. D. four times the original heat. 7. The wires used in a heating element are usually made of A. copper. C. aluminum. B. steel. D. Nichrome. 8. Why does a thermostat blade bend when heated or cooled? A. It is made of two different materials. B. There is a difference in temperature between the blade ends. C. Different currents are applied to each end. D. Mechanical pressure is caused by the high resistance. 9. When you are checking an electric heating appliance, the first test made should be for A. excessive leakage. C. an open circuit. B. the normal voltage supply. D. low resistance.10. Why should you NOT repair heating elements by soldering? A. Solder does not conduct electric current. B. Solder joints are mechanically too weak. C. Solder melts at the operating temperature of the heater. D. Soldered joints have too high a resistance.11. What type of selector switch can be used to control the heat output of three elements connected in parallel? A. SPST switch C. DPDT switch B. DPST switch D. Shorting-bar-type switch12. Thermostats used in electric irons differ from those in small room heaters in that they are A. smaller in size. C. connected directly to the appliance plug. B. operative at higher temperatures. D. mechanically more fragile.
Examination 8713. How can you clean out the scales in an electric iron without taking the iron apart? A. By blowing out the holes with compressed air B. By scraping the tank and tubes with a drill bit C. By brushing the clogged tubes with a stiff wire brush D. By rinsing the tank and holes with a water-diluted chemical14. Bus bars are used in an electric iron as A. thermostat supports. B. heat-adjusting resistors. C. connectors between the thermostat and the element. D. electrical terminals.15. The water in a spray iron is prevented from returning to the tank by the action of a A. suction tube. C. water pump. B. check valve. D. pressure spring.16. The heating element in an electric iron is in good working order if the resistance across the terminals of the element reads approximately A. 0 ohms. C. 120 ohms. B. 15 ohms. D. 1000 ohms.17. Why does the heat of the heating element stop when the desired temperature in an electric iron is reached? A. The thermostat blade opens electrical contacts. B. The circuit through the element is closed. C. The switch bypasses the thermostat. D. The contacts on the blade touch.18. Jumpering out the resistors in a resistance-controlled three-speed fan will cause the motor to A. run at highest speed. C. run at lowest speed. B. run at medium speed. D. stop immediately.19. A fan equipped with a gearbox is capable of A. running at three speeds. C. oscillating from side to side. B. being tilted downward. D. reversing the direction of the motor.20. If the fan blades rattle while the fan is turning, you can stop the noise by A. oiling the blades. B. adjusting the blade angles and the blade tip position. C. tightening the motor end bells and motor mounts. D. cleaning the blade surfaces.
88 Examination21. The recommended way to hold a loose hub on a fan is by A. riveting. C. welding. B. soldering. D. cementing.22. Quiet operation of a fan depends mostly upon the A. weight of the blades. C. motor balance. B. material of the blades. D. balance of the blades.23. The blades of small fans are made of A. aluminum. C. tin. B. steel. D. copper.24. A modern variable-speed fan does NOT use A. a tapped inductor. C. an electronic speed control. B. a multiple-winding motor. D. a dropping resistor.25. An attic fan, or power ventilator, may have its power inadvertently tapped from A. an upstairs bathroom. C. a basement service. B. an attic lighting circuit. D. an air conditioning circuit.