<ul><li>Prepare for ASE Heating and Air Conditioning (A7) certification test content areas: </li></ul><ul><li>— “ A”(Air Conditioning System Diagnosis and Repair), content area </li></ul><ul><li>— “ B” (Refrigeration System Component Diagnosis and Repair), content area </li></ul><ul><li>— “ C” (Heating and Engine Cooling Systems Diagnosis and Repair, content area </li></ul>OBJECTIVES: After studying Chapter 50, the reader should be able to: Continued
<ul><li>Prepare for ASE Heating and Air Conditioning (A7) certification test content areas: </li></ul><ul><li>— “ D” (Operating Systems and Related Controls Diagnosis and Repair), and content area </li></ul><ul><li>— “ E” (Refrigeration, Recovery, Recycling, and Handling). </li></ul><ul><li>Diagnose lack of heat problems. </li></ul>OBJECTIVES: After studying Chapter 50, the reader should be able to: Continued
<ul><li>List the air-conditioning system performance check procedures. </li></ul><ul><li>Discuss methods used to locate the source of an air-conditioning system leak. </li></ul><ul><li>Describe how to recover, evacuate, and recharge an air-conditioning system. </li></ul><ul><li>Discuss what is necessary to retrofit a CFC-12 system to to use HFC-134a refrigerant. </li></ul>OBJECTIVES: After studying Chapter 50, the reader should be able to:
HVAC DIAGNOSTIC PROCEDURE <ul><li>When diagnosing a heating and air-conditioning system problem, most vehicle manufacturers recommend the following steps: </li></ul>Continued Step #1 Verify the customer complaint ( concern ) Sometimes the customer does not understand how the system is supposed to work or does not explain the fault clearly. Verifying means that the tech can verify that the problem has been corrected after service. Step #2 Do a thorough visual inspection HVAC problems are often found by looking carefully at all of the components, checking for obvious faults or damage due to an accident or road debris. Step #3 Check for diagnostic trouble codes Many systems use sensors and actuators, which are computer controlled.
<ul><li>Step #4 Check for related technical service bulletins ( TSBs ) If there has been a bulletin released to solve a known problem, it saves time knowing what to do rather than trying to find and correct. </li></ul><ul><li>Step #5 Determine the root cause Find and correct the root cause of the problem. Low refrigerant level means there was a leak in the system. Finding and correcting the leak correcting the root cause. </li></ul><ul><li>Step #6 Verify the repair Drive the vehicle under similar conditions which caused the customer to complain and verify that the concern has been corrected. </li></ul>
HEATER DIAGNOSIS <ul><li>Most heat absorbed from the engine by the cooling system is wasted. </li></ul>Figure 50–1 The heater core is mounted inside a heater plenum chamber where air passes over it to absorb heat from the warmed engine coolant. Some of this heat is recovered by the vehicle heater. Air is passed across the heater fins and sent to the passenger compartment. In some vehicles, the heater and air conditioning work in series to maintain vehicle compartment temperature.
HEATER PROBLEM DIAGNOSIS <ul><li>When the vehicle’s heater does not produce the desired amount of heat, many owners and technicians replace the thermostat before doing any other troubleshooting. Many other causes besides a defective thermostat can result in lack of heat from the heater. To determine the exact cause, follow this procedure: </li></ul>Continued Step #1 If the engine is up to proper operating temperature, the upper radiator hose should be too hot for you to keep your hand on it. The hose should also be pressurized. <ul><li>If the hose is not hot enough, replace thermostat. </li></ul><ul><li>If the hose is not pressurized, test it. Replace the pressure cap if it will not hold specified pressure. </li></ul><ul><li>If okay, see step 2. </li></ul>
<ul><li>Step #2 With the engine running, feel both heater hoses. (Heater should be set to the maximum heat position.) Both hoses should be too hot to hold. If both hoses are warm (not hot) or cool, check the heater control valve for proper operation. If one hose is hot and the other (return) is just warm or cool, remove both hoses from the heater core or engine and flush the heater core with a garden hose. </li></ul>HINT: Heat from the heater that “comes and goes” is most likely the result of low coolant level. Usually with the engine at idle, there is enough coolant flow through the heater at higher engine speeds, however, the circulation of coolant through the heads and block prevents sufficient flow through the heater.
If the evaporator water drip tube becomes clogged with mud, leaves, or debris, water will build up inside the evaporator housing and spill out onto the carpet on the passenger side. Customers often think the windshield or door seals are leaking. Most evaporator water drains are not visible unless the vehicle is hoisted. Water on the Carpet? Check the Evaporator Water Drain.
HEATER TROUBLE DIAGNOSIS <ul><li>Lack of heat from the heater or heat coming out of the wrong vents can be a dangerous and uncomfortable problem. The first step in the diagnostic process is to perform a thorough visual inspection and perform simple tests. </li></ul>Continued <ul><li>Check the coolant level Low coolant level can cause a lack of heat from the heater. It can also cause occasional loss of heat. </li></ul>CAUTION: Do not remove the radiator cap when the engine is hot. Allow the vehicle to sit several hours before removing the pressure cap to-check the radiator coolant level.
<ul><li>Carefully touch the upper radiator hose with the engine running On most vehicles, the temperature of the hose should be so hot that you cannot keep your hand on it (between 190° to 220°F [88° to 104°C]). </li></ul>Continued NOTE: An infrared pyrometer can be used to measure the temperature of the upper radiator hose and the area around the thermostat housing. Results : If the upper radiator hose is not too hot to hold, then the engine thermostat is defective. If the radiator hose is too hot to handle, then the lack of heat from the heater is not due to a lack of hot water in the engine.
<ul><li>Carefully touch the heater hoses Both heater hoses should also be too hot to keep your hands on the hoses. This test confirms that engine coolant is able to flow from the engine to and through the heater core and return to the engine. See Figure 50–2. </li></ul>Results : (a) If neither heater hose is hot to the touch, it is likely there is an air pocket in the heater that is preventing the flow of coolant into the heater core. (b) If only one heater hose is hot to the touch, then the heater core is likely to be clogged or partially clogged. A clogged heater core would prevent enough hot coolant from circulating through the heater core to provide adequate heat to the passenger compartment. Continued
Figure 50–2 A heater control valve. This valve is normally open, allowing engine coolant to flow through the heater core. When the air conditioning is switched to maximum cooling, the valve shuts off the flow of coolant to the heater. Continued
<ul><li>A common problem involves airflow from the defroster ducts even though the selector lever is in other positions. The defrost setting is the default position in event of a failure with the vacuum supply. Defrost position is used because it is the safest position. For safety, the windshield must remain free from frost. Heat is also supplied to the passenger compartments through defrost ducts and the heater vents at floor level. </li></ul>Defrost All the Time? Check the Vacuum If the airflow is mostly directed to the windshield, check under the hood for a broken, disconnected, or missing vacuum hose. Check the vacuum reserve container for cracks or rust (if metal) that could prevent it from holding vacuum. Check all vacuum hose connections at the intake manifold and trace each carefully, inspecting for cracks, splits, or softened areas that may indicate a problem.
HINT: This problem of incorrect airflow inside the vehicle often occurs after another service procedure has been performed, such as spark plug replacement. The movement of the technician’s body and arms can cause a hose to be pulled loose or a vacuum fitting to break without the service technician being aware that anything wrong has occurred. NOTE: An air bubble could be lodged in the heater core. This is a common especially if coolant has been recently replaced. Failure to properly “burp” the air from the cooling system can cause a pocket of air to remain trapped in the heater core, preventing coolant from flowing. To check a radiator or condenser for possible clogged or restricted areas, simply touch the outside of the unit with your hand. Any cool spots indicate that the radiator or condenser is clogged in that cool area. The Hand Test
<ul><li>The first step in being certain there is no air in the cooling system is to try to avoid getting air into the system in the first place during cooling system service. If the engine is equipped with bleeder valves near the high spots of the cooling system, these valves should be open when refilling the radiator. Any trapped air will always travel to the highest portion of the cooling system and escape out of these bleeder openings. </li></ul>How Can You Easily Burp Air From the Cooling System? Figure 50–3 Many engines are equipped with a bleeder valve to permit a technician to bleed any trapped air from the cooling system. The valve is loosened as coolant is poured into the system. Because air is lighter than coolant, the air tends to float toward the highest part of the cooling system. Close the valves as soon as coolant is observed coming out of the valve opening. Part 1
<ul><li>If the cooling system is not equipped with bleeder valves, fill the cooling system as full as possible and then start the engine. With the radiator cap removed, the coolant level will often rise as trapped air expands, then drop down as the air escapes out of the radiator neck opening. Air can still remain trapped. To help speed the process, try installing the radiator cap just to the first notch. (In this position the radiator cap is closed, but will not seal enough to allow pressure to build in the cooling system.) </li></ul>To help force any trapped air from the cooling system, simply drive the vehicle normally for several miles. By driving the vehicle under load, the engine will warm up faster and the thermostat will open allowing the coolant to flow from the engine and through the radiator. Any trapped air is then released into the radiator where it can easily escape through the unsealed radiator cap. After filling the radiator, securely tighten the radiator cap and test-drive the vehicle to verify proper operation. How Can You Easily Burp Air From the Cooling System? Part 2
A common customer complaint is a lack of heat from the heater but only while driving, even through there seems to be plenty of heat when the engine is at idle speed and the vehicle is stopped. This is a classic symptom of low coolant level . The lower than normal coolant level in the radiator prevents enough flow to supply the heater core. When the engine speed is reduced, the water pump turns slower and coolant can more easily flow through the heater core resulting in heat from the heater. As the engine speed increases, the water pump speed also increases. Be-cause there is less than the proper amount of coolant in the system, the water pump will only be able to supply coolant through the engine (a path of lower resistance). Hot/Cold/Hot/Cold Heater Diagnosis
CHECKING A/C SYSTEM PERFORMANCE <ul><li>The first step in the diagnosis of any cooling system problem is to verify the complaint (concern). </li></ul>Step #1 Start the engine and turn the A/C system to maximum with the engine operating between 1500 and 2000 rpm with the doors open. Operate the system for 5 to 10 minutes. Continued Figure 50–4 Many older CFC-12 systems are equipped with a sight glass either on or near the receiver-drier. A fully-charged (or completely empty) system is indicated by a clear sight glass. Bubbles or foam indicate that the system is not fully charged. An empty system may have oil streaks on the sight glass being moved by the vapor remaining in the system. Step #2 Verify by visual inspection that the A/C compressor clutch is engaged. Check the sight glass if the vehicle is so equipped
<ul><li>Step #3 Place an air-conditioning thermometer in the A/C vent near the center of the vehicle. Wait several minutes to allow the system to reach maximum output and observe the thermometer. </li></ul>Continued <ul><li>If 35° to 45°F (2° to 7°C) ; system functioning OK. Continue a thorough visual inspection looking for any faults that may cause </li></ul><ul><li>If over 45°F (7°C) , continue with pressure gauge testing (Step 4). </li></ul>HINT: If the A/C compressor clutch cannot be observed, have an assistant turn the air conditioning on and then off and listen for the “click” of the A/C compressor clutch. Step #4 Identify the refrigerant . Before connecting the pressure gauges or performing any other service to an automotive air-conditioning system, verify the refrigerant that is presently in the system. Connect a refrigerant identification machine to the system. See Figure 50-5.
Figure 50–5 A typical refrigerant identification machine. The readout indicates what kind of refrigerant is in the system. If a blend or some other contaminated refrigerant is discovered, it should be recovered and stored in a separate container to keep it from contaminating fresh refrigerant. Continued
<ul><li>Step #5 Connect both high-pressure and low-pressure gauges to the service ports . The low-side pressure should be about 25 to 35 psi. The high-side pressure should be about 150 to 200 psi. Compare your readings to the normal and abnormal readings in the following chart. See Figures 50–6 and 50–7. </li></ul>Continued See the chart on Page 574 of your textbook.
Figure 50–6 (a) Both high-pressure (red) and low-pressure (blue) hoses have been attached to the vehicle. (b) High-side pressure can be compared to the temperature of the outlet from the compressor. Here a service tech is using an infrared pyrometer to measure the temperature. Figure 50–7 Hot refrigerant condenses in the condenser when it loses its heat to the outside air. Note how the level of the liquid line changes when undercharged or overcharged.
<ul><li>Temperature and pressure are directly related in A/C systems. As ambient temperature increases, high-side pressure must also increase to have heat transfer at the condenser. High - side pressure is directly related to the amount of heat that needs to be removed, and the heat transfer at the condenser. Low - side pressure indicates the boiling point of the evaporator. If pressure is too high, the boiling point and temperature of the evaporator are too high. Low-side pressure too low indicates the evaporator is too cold or there is not enough boiling refrigerant in the evaporator to remove an adequate amount of heat. See 50–8. </li></ul>TEMPERATURE AND PRESSURE MEASUREMENTS Continued
<ul><li>Heat transfer at the condenser is usually the cause of high-side pressure that is too high. The number one cause of poor heat transfer is lack of airflow across the condenser. </li></ul>Figure 50–8 The average R-134a pressure–temperature readings during a performance test. The high-side pressure of R-12 systems will be lower at higher temperatures. See the chart on Page 575 of your textbook. Continued
<ul><li>Another cause of excessive high-side pressure is contamination with a different refrigerant. Mixing R-12 and R-134a raises condensing pressure of the mixture. Pressures go really high with R-22. At 150°F, the pressure of R-12 is 235 psi (1,620 kPa), R-134a is 263 psi (1,813 kPa), and R-22 is 381 psi (2,627 kPa). This is an important reason to use a refrigerant identifier. As compressor efficiency is reduced, the high side decreases, and the low side increases. The function of the compressor is to pull down the low side and push up the high side. When the compressor is failing, it does not do either job well. Always look at both the high- and low-side pressures when diagnosing a problem. See Figures 50–9 through 50–11. </li></ul>Continued
Figure 50–9 When both low- and high-side pressures are low, the system is undercharged with refrigerant. Continued
Figure 50–10 Both low- and high-side pressures higher than normal indicate that the system is overcharged with refrigerant. Continued
Figure 50–11 Lack of proper airflow across the condenser is usually the cause of this condition.
<ul><li>For example: </li></ul><ul><li>+ 100 </li></ul><ul><li>185 PSI typical normal high-side pressure . </li></ul>This is common on a vehicle equipped with a cycling clutch orifice tube (CCOT) system that is low on refrigerant charge. With a normal charge, the low-side pressure should be 15 to 35 PSI and the clutch should be on for 45 to 90 seconds and be off for only about 15 to 30 seconds. What’s Wrong When the A/C Compressor Clutch Cycles On and Off Rapidly? A quick and easy way to determine the correct high-side pressure is to add 100 to the ambient air temperature in Fahrenheit. High Side Pressure Tip 85ºF outside air temperature
<ul><li>A clogged orifice tube is a common air-conditioning system failure. A clogged tube blocks refrigerant flow through the evaporator, which causes reduced cooling of the passenger compartment. To check for a possible restriction in the system, follow these easy steps: </li></ul>Clogged Orifice Tube Test Step # 1 Connect the A/C pressure gauge to both low- and high-side pressure fittings. Step # 2 Operate the A/C system for 5 to 10 minutes. Step # 3 Shut off the A/C system and watch the pressure gauges. If pressures do not equalize quickly, there is a restriction in the system. NOTE: To locate a restriction in the system, feel along the system lines. The restriction exists at the point of greatest temperature difference.
Clogged Orifice Tube Test - Part 2 Figure 50–12 A clogged orifice tube. Figure 50–13 Assortment of orifice tubes. Note that each is color coded and identified on the lid of the assortment. Even though some technicians have purposely installed an orifice tube with a larger opening in an attempt to increase cooling, it is always safe to use the exact orifice tube specified for the vehicle being serviced.
To test the expansion valve, start the engine and allow the A/C system to function with the control set to “recirculate.” Using a CO2 fire extinguisher, blast the expansion valve with CO2 . The valve should close and the low side pressure should go into a vacuum. If the low-side pressure does not go into a vacuum, the expansion valve is faulty and should be replaced. The Fire Extinguisher Test Figure 50–14 (a) A CO 2 fire extinguisher equipped with the fittings necessary to test the operation of an expansion valve. (b) The size of the opening at the end of the hose determines how much CO 2 is released to cool the expansion valve temperature sensor bulb. (a) (b)
<ul><li>Then the tech discovered the cause of the lack of airflow—the evaporator was covered with oily dirt. The tech recovered the refrigerant and removed the evaporator. Apparently, the evaporator had a small refrigerant leak that allowed the refrigerant oil to coat the fins of the evaporator. </li></ul>The owner of an older Buick complained that the blower motor must be defective because the air no longer flowed from the air-conditioning vents as it should. A check of the blower motor circuit revealed that the blower motor was working. To confirm the operation of the blower, the resistor pack was removed and air flowed out of the opening. The Clogged Evaporator Problem Figure 50–15 A partially clogged evaporator. Any dirt in the air stuck to the evaporator until the dirt almost completely blocked the airflow. Replacing the evaporator and recharging the system fixed problem.
<ul><li>Normal operation Both temperatures about the same </li></ul>To check the state of charge of an orifice tube system, use one hand and touch the evaporator side of the orifice tube. Touch the other hand to the inlet to the accumulator. The following conditions can be determined by the temperature of these two locations: The Touch, Feel Test Undercharged condition Accumulator temperature higher (warmer) than the orifice tube temperature High pressure means that the temperature of the component or line will also be high (hot). Low pressure means that the temperature of the component or line will also be low (cold).
Figure 50–16 If the system is fully charged, the outlet temperature of the line leaving the evaporator should be about the same as the temperature of the line entering the evaporator after the expansion valve. The low-pressure cycling switch usually has to be disconnected and a jumper wire used to connect the two electrical terminals allowing the compressor to run if the system is low on charge.
<ul><li>Leak Detection If the A/C system is low on a charge of refrigerant, the sources of the leak should be found and corrected. Several different methods of leak detection: </li></ul>Figure 50–17 Typical electronic refrigerant leak detector. Many are capable of detecting either CFC-12 or HFC-134a. Continued <ul><li>Visual inspection Look for oily areas formed when refrigerant leaks and some refrigerant oil is lost. It is this oil that indicates a refrigerant leak. </li></ul><ul><li>Electronic leak detector Many of these units can detect both CFC-12 and HFC-134a. The detector will sound a tone if a leak is detected. </li></ul>
<ul><li>Dye in the refrigerant Dye is added to refrigerant to help the tech spot a leak in the refrigerant system. This method works well except for leaks in the evaporator, which are usually not visible. </li></ul>Figure 50–18 A black light being used to look for refrigerant leaks after a fluorescent dye was installed in the system. <ul><li>Soap solution Mix a few drops of liquid soap or detergent into a small glass of water. </li></ul>Use a small brush or spray bottle to apply the soapy solution to fittings and other areas such as the condenser and compressor If the system is empty, pressurize it with dry-nitrogen.
Many air-conditioning systems form mildew inside the evaporator housing due to the moist condition that exists in this area. If a “wet” smell is noticed, the mold and mildew may be the cause and a biocide will need to be used to correct the problem. The Smell Test A quick-and-easy test to check whether the evaporator is leaking refrigerant is to remove the blower motor resistor pack. The blower motor resistor pack is almost always located directly “downstream” and near the blower motor. Removing the blower motor resistor pack gives access to the area near the evaporator. Inserting the probe of a leak detector into this open area allows the detector to test the air close to the evaporator. Leak Testing the Evaporator
SUMMARY <ul><li>The upper radiator hose and both heater hoses should be hot to the touch on a warm engine. </li></ul><ul><li>Failure to properly “burp” air from the cooling system after servicing can cause a lack of heat from the heater. </li></ul><ul><li>A sight glass is found on many older-model vehicles equipped with CFC-12. If the sight glass is cloudy, then the system charge is low. </li></ul><ul><li>Normal air-vent temperature for a properly operating air conditioning system is 35° to 45°F (2° to 7°C). </li></ul>Continued
SUMMARY <ul><li>An expansion valve or orifice tube is used to allow the liquid refrigerant to expand into a gas inside the evaporator. Heat is absorbed by the refrigerant as it changes state from a liquid to a gas and the evaporator becomes cold. </li></ul><ul><li>The outlet of the evaporator should be about the same temperature as the evaporator side of the orifice tube if the system is operating properly. </li></ul><ul><li>Refrigerant leaks can be detected by visual inspection, an electronic leak detector, dye, or a soap solution. </li></ul><ul><li>A partially clogged evaporator can cause a lack of cooling. </li></ul>Continued ( cont. )
SUMMARY <ul><li>The temperatures of the inlet and outlet lines to and from the evaporator should be about the same if the system is fully charged. </li></ul><ul><li>If the compressor clutch is cycling on and off rapidly on a cycling clutch-type system, the most common cause is low on refrigerant. </li></ul><ul><li>Typical high side pressure can be estimated by adding 100 to the outside temperature. </li></ul>( cont. )