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Halderman ch058 lecture
 

Halderman ch058 lecture

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  • Figure 58-1 Two horns are used on this vehicle. Many vehicles use only one horn, often hidden underneath the vehicle.
  • Figure 58-2 A typical horn circuit. Note that the horn button completes the ground circuit for the relay.
  • Figure 58-3 Horns typically mount to the radiator core support or bracket at the front of the vehicle.
  • Figure 58-4 A circuit diagram is necessary to troubleshoot a windshield wiper problem.
  • Figure 58-5 The motor and linkage bolt to the body and connect to the switch with a wiring harness.
  • Figure 58-6 A typical wiper motor with the housing cover removed. The motor itself has a worm gear on the shaft that turns the small intermediate gear, which then rotates the gear and tube assembly, which rotates the crank arm (not shown) that connects to the wiper linkage.
  • Figure 58-7 A wiring diagram of a two-speed windshield wiper circuit using a three-brush, two-speed motor. The dashed line for the multifunction lever indicates that the circuit shown is only part of the total function of the steering column lever.
  • Figure 58-8 A wiring diagram of a three-speed windshield wiper circuit using a two-brush motor, but both a series-wound and a shunt field coil.
  • Figure 58-9 A variable pulse rate windshield wiper circuit. Notice that the wiring travels from the passenger compartment through pass-through grommets to the underhood area.
  • Figure 58-10 A wiper motor connector pin chart.
  • Figure 58-11 The wiper motor and linkage mount under the cowl panel on many vehicles.
  • Figure 58-12 A single wiper arm mounts directly to the motor on most rear wiper applications.
  • Figure 58-14 Disconnect the hose at the pump and operate the switch to check a washer pump.
  • Figure 58-15 Washer pumps usually install into the reservoir and are held in place with a retaining ring.
  • Figure 58-16 A typical rain sensing module located on the inside of the windshield near the inside rearview mirror.
  • Figure 58-17 The electronics in the rain sense wiper module can detect the presence of rain drops under various lighting conditions.
  • Figure 58-18 A squirrel cage blower motor. A replacement blower motor usually does not come equipped with the squirrel cage blower, so it has to be switched from the old motor.
  • Figure 58-19 A typical blower motor circuit with four speeds. The three lowest fan speeds (low, medium-low, and medium-high) use the blower motor resistors to drop the voltage to the motor and reduce current to the motor. On high, the resistors are bypassed. The “high” position on the fan switch energizes a relay, which supplies the current for the blower on high through a fusible link.
  • Figure 58-20 A typical blower motor resistor pack used to control blower motor speed. Some blower motor resistors are flat and look like a credit card and are called “credit card resistors”.
  • Figure 58-21 A brushless DC motor that uses the body computer to control the speed. (Courtesy of Sammy’s Auto Service, Inc.)
  • Figure 58-22 Using a mini AC/DC clamp-on multimeter to measure the current draw of a blower motor.

Halderman ch058 lecture Halderman ch058 lecture Presentation Transcript

  • HORN, WIPER, AND BLOWER MOTOR CIRCUITS 58
  • Objectives
    • The student should be able to:
      • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “G” (Horn and Wiper/Washer Diagnosis and Repair) and content area “H” (Accessories Diagnosis and Repair).
      • Describe how the horn operates.
      • List the components of a wiper circuit.
  • Objectives
    • The student should be able to:
      • Explain how the blower motor can run at different speeds.
      • Discuss how to diagnosis faults in the horn, wiper, and blower motor circuits.
  • HORNS
  • Horns
    • Purpose and Function
      • Horns are electric devices that emit a loud sound
      • Several different tones ranging from 1,800 to 3,550 Hz
  • Figure 58-1 Two horns are used on this vehicle. Many vehicles use only one horn, often hidden underneath the vehicle.
  • Horns
    • Horn Circuits
      • Horns usually operate on full battery voltage
      • Most vehicles use a horn relay
  • Horns
    • Horn Circuits
      • With a relay the horn button on the steering wheel completes a circuit to ground that closes the relay
      • The heavy current flow travels from the relay to the horn
  • Horns
    • Horn Circuits
      • Without a relay, the high current flows through the steering wheel horn switch
      • The relay is also connected to the body control module, which “beeps” the horn when the vehicle is locked or unlocked, using the key fob remote
  • Figure 58-2 A typical horn circuit. Note that the horn button completes the ground circuit for the relay.
  • Horns
    • Horn Operation
      • A horn is an actuator that converts an electrical signal to sound
      • The horn circuit includes an armature (a coil of wire) and contacts attached to a diaphragm
  • Horns
    • Horn Operation
      • The arm causes the diaphragm to move up which opens a set of contact points that de-energize the arm circuit
  • Horns
    • Horn Operation
      • As the diaphragm moves down, the contact points close, reenergize the arm circuit, and the diaphragm moves up again, causing the diaphragm to vibrate at an audible frequency
  • Horns
    • Horn Diagnosis System
      • There are four types of horn failure:
        • No horn operation
        • Intermittent operation
  • Horns
    • Horn Diagnosis System
      • There are four types of horn failure:
        • Constant operation
        • Weak or low volume sound
  • Horns
    • Horn Diagnosis System
      • If the horn does not work at all, check the following:
        • Burned fuse or fusible link
          • Open circuit
          • Defective horn
  • Horns
    • Horn Diagnosis System
      • If the horn does not work at all, check the following:
        • Burned fuse or fusible link
          • Faulty relay
          • Defective horn switch
  • Horns
    • Horn Diagnosis System
      • If the horn does not work at all, check the following:
        • Burned fuse or fusible link
          • Poor ground (horn mounting)
          • Corroded or rusted electrical connector
  • Horns
    • Horn Diagnosis System
      • If the horn operates intermittently, check for the following:
          • Loose contact at the switch
          • Loose, frayed, or broken wires
          • Defective relay
  • Horns
    • Horn Sounds Continuously
      • Horn switch contacts that are stuck closed or a short-to-ground on the control circuit could cause the horn to sound continuously
      • There could be a defective horn switch or a faulty relay
  • Horns
    • Horn Sounds Continuously
      • Disconnect the horn and check continuity through the horn switch and relay to locate the source of the problem
  • Horns
    • Inoperative Horn
      • Use a fused jumper wire and connect one end to the positive post of the battery and the other end to the wire terminal of the horn itself
  • Horns
    • Inoperative Horn
      • If the horn works with jumper wires connected, check ground wires and connections
        • If the horn works, the problem is in the circuit supplying current to the horn
  • Horns
    • Inoperative Horn
      • If the horn works with jumper wires connected, check ground wires and connections
        • If the horn does not work, the horn itself could be defective or the mounting bracket may not be providing a good ground
  • Horns
    • Horn Service
      • Circuit tests are done to determine if the horn, relay, switch, or wiring is the source of the failure
        • Switch and relay
        • Circuit testing
  • Horns
    • Horn Service
      • Circuit tests are done to determine if the horn, relay, switch, or wiring is the source of the failure
        • Circuit testing
          • STEP 1: Make sure the fuse or fusible link is good.
  • Horns
    • Horn Service
      • Circuit tests are done to determine if the horn, relay, switch, or wiring is the source of the failure
        • Circuit testing
          • STEP 2: Check that the ground connections for the horn are clean and tight.
  • Horns
    • Horn Service
      • Circuit tests are done to determine if the horn, relay, switch, or wiring is the source of the failure
        • Circuit testing
          • STEP 3: On a system with a relay, test the power output circuit and the control circuit. When no relay is used, a connection to the steering wheel is made with a double contact slip ring. Test points on this system are similar to those of a system with a relay, but there is no control circuit.
  • Horns
    • Horn Service
      • CAUTION: If steering wheel removal is required for diagnosis or repair of the horn circuit, follow service information procedures for disarming the airbag circuit prior to steering wheel removal, and for the specified test equipment to use.
  • Horns
    • Horn Replacement
      • It may be necessary to remove the grille or other parts to access the horn mounting screws
      • Attempt to use a horn of the same tone as the original (tone is usually indicated by a number or letter stamped on the body of the horn)
  • Horns
    • Horn Replacement
      • Remove the fasteners and lift the old horn from its mounting bracket
      • Clean the attachment area on the mounting bracket and chassis
  • Figure 58-3 Horns typically mount to the radiator core support or bracket at the front of the vehicle.
  • WINDSHIELD WIPER AND WASHER SYSTEM
  • Windshield Wiper and Washer System
    • Purpose and Function
      • Windshield wipers are used to keep the viewing area of the windshield clean of rain
      • Some vehicles combine the windshield wiper and windshield washer functions into a single system
  • Windshield Wiper and Washer System
    • Purpose and Function
      • Some vehicles have a rear window wiper and washer system
      • All windshield and rear window wiper and washer systems operate in a similar fashion
  • Windshield Wiper and Washer System
    • Computer Controlled
      • Most wipers since the 1990s have used the body computer to control the actual operation of the wiper
  • Figure 58-4 A circuit diagram is necessary to troubleshoot a windshield wiper problem.
  • Windshield Wiper and Washer System
    • Wiper and Washer Components
      • Wiper motor
      • Gearbox
      • Wiper arms and linkage
  • Windshield Wiper and Washer System
    • Wiper and Washer Components
      • Washer pump
      • Hoses and jets (nozzles)
      • Fluid reservoir
  • Windshield Wiper and Washer System
    • Wiper and Washer Components
      • Combination switch
      • Wiring and electrical connectors
      • Electronic control module
  • Figure 58-5 The motor and linkage bolt to the body and connect to the switch with a wiring harness.
  • Windshield Wiper and Washer System
    • Windshield Wiper Motors
      • Windshield wipers ordinarily use a special two-speed electric motor
  • Windshield Wiper and Washer System
    • Windshield Wiper Motors
      • Most are compound-wound motors, which provide two different speeds
        • Series-wound field
        • Shunt field
  • Windshield Wiper and Washer System
    • Windshield Wiper Motors
      • Most wiper motors use a permanent magnet motor with a low speed brush and a high speed brush
      • The brushes connect the battery to the internal windings of the motor, and allow for two different motor speeds
  • Windshield Wiper and Washer System
    • Windshield Wiper Motors
      • The variable-delay wipers (also called pulse wipers) use an electronic circuit with a variable resistor that controls the time of the charge and discharge of a capacitor
  • Figure 58-6 A typical wiper motor with the housing cover removed. The motor itself has a worm gear on the shaft that turns the small intermediate gear, which then rotates the gear and tube assembly, which rotates the crank arm (not shown) that connects to the wiper linkage.
  • Figure 58-7 A wiring diagram of a two-speed windshield wiper circuit using a three-brush, two-speed motor. The dashed line for the multifunction lever indicates that the circuit shown is only part of the total function of the steering column lever.
  • Figure 58-8 A wiring diagram of a three-speed windshield wiper circuit using a two-brush motor, but both a series-wound and a shunt field coil.
  • Figure 58-9 A variable pulse rate windshield wiper circuit. Notice that the wiring travels from the passenger compartment through pass-through grommets to the underhood area.
  • Windshield Wiper and Washer System
    • Hidden Wipers
      • Some vehicles are equipped with wipers that become hidden when turned off
      • These wipers are also called depressed wipers
  • Windshield Wiper and Washer System
    • Hidden Wipers
      • The gearbox has an additional linkage arm to provide depressed parking for hidden wipers
  • Windshield Wiper and Washer System
    • Windshield Wiper Diagnosis
      • To determine if there is an electrical or mechanical problem, access the motor assembly and disconnect the wiper arm linkage from the motor and gearbox
  • Windshield Wiper and Washer System
    • Windshield Wiper Diagnosis
      • This procedure may involve:
        • Removing body trim panels at the base of the windshield to gain access to the linkage connectors
  • Windshield Wiper and Washer System
    • Windshield Wiper Diagnosis
      • This procedure may involve:
        • Switching the motor on to each speed (If the motor operates at all speeds, the problem is mechanical. If the motor still does not operate, the problem is electrical.)
  • Windshield Wiper and Washer System
    • Windshield Wiper Diagnosis
      • If the wiper motor does not run at all, check for the following:
        • Grounded or inoperative switch
        • Defective motor
  • Windshield Wiper and Washer System
    • Windshield Wiper Diagnosis
      • If the wiper motor does not run at all, check for the following:
        • Circuit wiring fault
        • Poor electrical ground connection
  • Windshield Wiper and Washer System
    • Windshield Wiper Diagnosis
      • If the motor operates but the wipers do not, check for the following:
        • Stripped gears in the gearbox or stripped linkage connection
  • Windshield Wiper and Washer System
    • Windshield Wiper Diagnosis
      • If the motor operates but the wipers do not, check for the following:
        • Loose or separated motor-to-gearbox connection
        • Loose linkage to the motor connection
  • Windshield Wiper and Washer System
    • Windshield Wiper Diagnosis
      • If the motor does not shut off, check for the following:
        • Defective park switch inside the motor
        • Defective wiper switch
  • Windshield Wiper and Washer System
    • Windshield Wiper Diagnosis
      • If the motor does not shut off, check for the following:
        • Poor ground connection at the wiper switch
  • Windshield Wiper and Washer System
    • Windshield Wiper Testing
      • Perform the following steps:
        • STEP 1: Refer to the circuit diagram or a connector pin chart to determine the test points for voltage measurements.
  • Windshield Wiper and Washer System
    • Windshield Wiper Testing
      • Perform the following steps:
        • STEP 2: Switch the ignition on and set the wiper switch to a speed at which the motor does not operate.
  • Windshield Wiper and Washer System
    • Windshield Wiper Testing
      • Perform the following steps:
        • STEP 3: Check for battery voltage available at the appropriate wiper motor terminal for the selected speed. If voltage is available to the motor, an internal motor problem is indicated. No voltage available indicates a switch or circuit failure.
  • Windshield Wiper and Washer System
    • Windshield Wiper Testing
      • Perform the following steps:
        • STEP 4: Check for proper ground connections.
  • Windshield Wiper and Washer System
    • Windshield Wiper Testing
      • Perform the following steps:
        • STEP 5: Check that battery voltage is available at the motor side of the wiper switch. If battery voltage is available, the circuit is open between the switch and motor. No voltage available indicates either a faulty switch or a power supply problem.
  • Windshield Wiper and Washer System
    • Windshield Wiper Testing
      • Perform the following steps:
        • STEP 6: Check for battery voltage available at the power input side of the wiper switch. If voltage is available, the switch is defective. Replace the switch. No voltage available to the switch indicates a circuit problem between the battery and switch.
    ?
  • Figure 58-10 A wiper motor connector pin chart.
  • Windshield Wiper and Washer System
    • Windshield Wiper Service
      • Bulkhead-mounted units are accessible from under the hood
      • The cowl panel needs to be removed to service a motor mounted in the cowl
  • Windshield Wiper and Washer System
    • Windshield Wiper Service
      • To remove the motor, disconnect the linkage, unplug the electrical connectors, and unbolt the motor
      • Move the wiper linkage through its full travel by hand to check for binding before installing the new motor
  • Windshield Wiper and Washer System
    • Windshield Wiper Service
      • Rear window wiper motors are generally located inside the rear door or the rear hatch panels
      • After removing the trim panel covering the motor, replacement is essentially the same as replacing the front wiper motor
  • Windshield Wiper and Washer System
    • Windshield Wiper Service
      • Steering column wiper switches require partial disassembly of the steering column for replacement
  • Figure 58-11 The wiper motor and linkage mount under the cowl panel on many vehicles.
  • Figure 58-12 A single wiper arm mounts directly to the motor on most rear wiper applications.
  • Windshield Wiper and Washer System
    • Pulse Wipe Systems
      • Windshield wipers that have a delay, or intermittent operation, feature are commonly called pulse wipe
  • Windshield Wiper and Washer System
    • Pulse Wipe Systems
      • Pulse wipe systems may rely on simple electrical controls or be controlled through a module
  • Windshield Wiper and Washer System
    • Pulse Wipe Systems
      • A typical pulse wiper system uses either a governor or a solid-state module that contains either a variable resistor or rheostat and capacitor
  • Windshield Wiper and Washer System
    • Pulse Wipe Systems
      • The following troubleshooting procedure applies to most models:
        • STEP 1: If the wipers do not run at all, check the wiper fuse, fusible link, or circuit breaker and verify that voltage is available to the switch.
  • Windshield Wiper and Washer System
    • Pulse Wipe Systems
      • The following troubleshooting procedure applies to most models:
        • STEP 2: Refer to a wiring diagram of the switch to determine how current is routed through it to the motor in the different positions.
  • Windshield Wiper and Washer System
    • Pulse Wipe Systems
      • The following troubleshooting procedure applies to most models:
        • STEP 3: Disconnect the switch and use fused jumper wires to apply power directly to the motor on the different speed circuits.
          • If the motor now runs, the problem is in the switch or module.
  • Windshield Wiper and Washer System
    • Pulse Wipe Systems
      • The following troubleshooting procedure applies to most models:
        • STEP 3: Disconnect the switch and use fused jumper wires to apply power directly to the motor on the different speed circuits.
          • Check for continuity in the circuit for each speed through the control-to-ground if the wiper motor runs at some, but not all, speeds.
  • Windshield Wiper and Washer System
    • Windshield Washer Operation
      • A washer pump is located in the washer reservoir
      • A momentary contact switch energizes the washer pump
  • Windshield Wiper and Washer System
    • Windshield Washer Operation
      • Washer pump switches are installed either on the steering column or on the instrument panel
      • The nozzles can be located on the bulkhead or in the hood
  • Windshield Wiper and Washer System
    • Windshield Washer Diagnosis
      • The following are possible causes of a faulty washer system:
        • Blown fuse or open circuit
        • Empty reservoir
        • Clogged nozzle
  • Windshield Wiper and Washer System
    • Windshield Washer Diagnosis
      • The following are possible causes of a faulty washer system:
        • Broken, pinched, or clogged hose
        • Loose or broken wire
        • Blocked reservoir screen
  • Windshield Wiper and Washer System
    • Windshield Washer Diagnosis
      • The following are possible causes of a faulty washer system:
        • Leaking reservoir
        • Defective pump
  • Windshield Wiper and Washer System
    • Windshield Washer Diagnosis
      • To diagnose the washer system, follow service information procedures that usually include the following:
        • STEP 1: To quick check any washer system, make sure the reservoir has fluid and is not frozen, and then disconnect the pump hose and operate the washer switch.
  • Windshield Wiper and Washer System
    • Windshield Washer Diagnosis
      • To diagnose the washer system, follow service information procedures that usually include the following:
        • STEP 2: If fluid squirts from the pump, the delivery system is at fault, not the motor, switch, or circuitry.
  • Windshield Wiper and Washer System
    • Windshield Washer Diagnosis
      • To diagnose the washer system, follow service information procedures that usually include the following:
        • STEP 3: If no fluid squirts from the pump, the problem is most likely a circuit failure, defective pump, or faulty switch.
  • Windshield Wiper and Washer System
    • Windshield Washer Diagnosis
      • To diagnose the washer system, follow service information procedures that usually include the following:
        • STEP 4: A clogged reservoir screen also may be preventing fluid from entering the pump.
  • Windshield Wiper and Washer System
    • Windshield Washer Diagnosis
      • NOTE: Always use good-quality windshield washer fluid from a closed container to prevent contaminated fluid from damaging the washer pump. Radiator antifreeze (ethylene glycol) should never be used in any windshield wiper system.
  • Figure 58-14 Disconnect the hose at the pump and operate the switch to check a washer pump.
  • Windshield Wiper and Washer System
    • Windshield Washer Service
      • When there is a problem with fluid delivery, check for:
        • Blocked, pinched, broken, or disconnected hose
  • Windshield Wiper and Washer System
    • Windshield Washer Service
      • When there is a problem with fluid delivery, check for:
        • Clogged nozzles
  • Windshield Wiper and Washer System
    • Windshield Washer Service
      • When there is a problem with fluid delivery, check for:
        • Blocked washer pump outlet
  • Windshield Wiper and Washer System
    • Windshield Washer Service
      • If the pump motor does not operate, check for battery voltage while operating the washer switch
        • If voltage is available and the pump does not run, check for continuity on the pump ground circuit
  • Windshield Wiper and Washer System
    • Windshield Washer Service
      • If the pump motor does not operate, check for battery voltage while operating the washer switch
        • If there is no voltage drop on the ground circuit, replace the pump motor
  • Windshield Wiper and Washer System
    • Windshield Washer Service
      • If the pump motor does not operate, check for battery voltage while operating the washer switch
        • If voltage is not available at the motor, check for power through the washer switch
  • Windshield Wiper and Washer System
    • Windshield Washer Service
      • If the pump motor does not operate, check for battery voltage while operating the washer switch
        • If voltage is available, the problem is in the wiring between the switch and pump
  • Windshield Wiper and Washer System
    • Windshield Washer Service
      • If the pump motor does not operate, check for battery voltage while operating the washer switch
        • Perform voltage drop tests to locate the fault
  • Windshield Wiper and Washer System
    • Windshield Washer Service
      • If the pump motor does not operate, check for battery voltage while operating the washer switch
        • Repair the wiring as needed and retest
  • Windshield Wiper and Washer System
    • Windshield Washer Service
      • Washer motors are not repairable and are simply replaced if defective
  • Figure 58-15 Washer pumps usually install into the reservoir and are held in place with a retaining ring.
  • RAIN SENSE WIPER SYSTEM
  • Rain Sense Wiper System
    • Parts and Operation
      • There are sensors located at the top interior of the windshield that determine and adjust the time delay based on the amount of moisture detected
      • A microprocessor sends a command to the body control module (BCM)
  • Rain Sense Wiper System
    • Parts and Operation
      • A housing with fine openings on the windshield side is fitted with eight convex clear plastic lenses
  • Rain Sense Wiper System
    • Parts and Operation
      • The unit contains four infrared (IR) diodes, two photocells, and a microprocessor
  • Rain Sense Wiper System
    • Parts and Operation
      • The IR diodes generate beams aimed by four of the lenses near the base of the module through the windshield
  • Rain Sense Wiper System
    • Parts and Operation
      • Four additional lenses near the top of the RSM are focused on the IR light beam on the outside of the windshield allowing the two photocells to sense changes in the intensity of the IR light beam
  • Rain Sense Wiper System
    • Parts and Operation
      • When sufficient moisture accumulates, the RSM detects a change in the monitored IR light beam intensity
      • The RSM processes the signal BCM over the data BUS to command a swipe of the wiper
  • Figure 58-16 A typical rain sensing module located on the inside of the windshield near the inside rearview mirror.
  • Figure 58-17 The electronics in the rain sense wiper module can detect the presence of rain drops under various lighting conditions.
  • Rain Sense Wiper System
    • Diagnosis and Service
      • If the rain sense wipers malfunction, be sure they are properly set and adjusted
      • Verify that the windshield wipers are functioning correctly at all speeds
  • BLOWER MOTOR
  • Blower Motor
    • Purpose and Function
      • The same blower motor moves air inside the vehicle for:
        • Air conditioning
        • Heat
  • Blower Motor
    • Purpose and Function
      • The same blower motor moves air inside the vehicle for:
        • Defrosting
        • Defogging
        • Venting of the passenger compartment
  • Blower Motor
    • Purpose and Function
      • The motor turns a squirrel cage-type fan, which is able to move air without creating a lot of noise.
  • Blower Motor
    • Purpose and Function
      • The fan switch controls the path followed by the current to the blower motor
  • Figure 58-18 A squirrel cage blower motor. A replacement blower motor usually does not come equipped with the squirrel cage blower, so it has to be switched from the old motor.
  • Blower Motor
    • Parts and Operation
      • The motor is usually a permanent magnet, one-speed motor that operates at its maximum speed with full battery voltage
  • Blower Motor
    • Parts and Operation
      • The switch gets current from the fuse panel with the ignition switch on, and directs full battery voltage to the motor for high speed and to the motor through resistors for lower speeds
  • Blower Motor
    • Variable Speed Control
      • The fan switch controls the path of current through a resistor pack to obtain different fan speeds
  • Blower Motor
    • Variable Speed Control
      • The electrical path can be:
        • Full battery voltage for high-speed operation
  • Blower Motor
    • Variable Speed Control
      • The electrical path can be:
        • Through one or more resistors to reduce the voltage and the current to the blower motor which then rotates at a slower speed
  • Blower Motor
    • Variable Speed Control
      • Resistors are located near the blower motor and mounted in the duct where the airflow can cool the resistors
  • Blower Motor
    • Variable Speed Control
      • Current flow through the resistor is controlled by the switch and often uses a relay to carry the heavy current (10 to 12 amperes) to power the fan
  • Blower Motor
    • Variable Speed Control
      • Normal operation includes:
        • Low speed
        • Medium speed
  • Blower Motor
    • Variable Speed Control
      • Normal operation includes:
        • Medium-high speed
        • High speed
  • Blower Motor
    • Variable Speed Control
      • NOTE: Most Ford and some other vehicles place the blower motor resistors on the ground side of the motor circuit. The location of the resistors does not affect the operation because they are connected in series.
  • Figure 58-19 A typical blower motor circuit with four speeds. The three lowest fan speeds (low, medium-low, and medium-high) use the blower motor resistors to drop the voltage to the motor and reduce current to the motor. On high, the resistors are bypassed. The “high” position on the fan switch energizes a relay, which supplies the current for the blower on high through a fusible link.
  • Figure 58-20 A typical blower motor resistor pack used to control blower motor speed. Some blower motor resistors are flat and look like a credit card and are called “credit card resistors”.
  • Figure 58-21 A brushless DC motor that uses the body computer to control the speed. (Courtesy of Sammy’s Auto Service, Inc.)
  • Blower Motor
    • Blower Motor Diagnosis
      • If the blower motor does not operate at any speed, the problem could be any of the following:
        • Defective ground wire or ground wire connection
  • Blower Motor
    • Blower Motor Diagnosis
      • If the blower motor does not operate at any speed, the problem could be any of the following:
        • Defective blower motor (not repairable; must be replaced)
  • Blower Motor
    • Blower Motor Diagnosis
      • If the blower motor does not operate at any speed, the problem could be any of the following:
        • Open circuit in the power-side circuit, including fuse, wiring, or fan switch
  • Blower Motor
    • Blower Motor Diagnosis
      • If the blower works on lower speeds but not on high speed, the problem is usually an inline fuse or high-speed relay
      • The blower motor is a sealed unit and must be replaced as a unit
  • Blower Motor
    • Blower Motor Diagnosis
      • The squirrel cage fan usually needs to be removed and attached to the replacement motor
  • Blower Motor
    • Blower Motor Diagnosis
      • If the blower motor operates normally at high speed but not at any of the lower speeds, the problem could be melted wire resistors or a defective switch
      • The blower motor can be tested using a clamp-on DC ammeter
  • Figure 58-22 Using a mini AC/DC clamp-on multimeter to measure the current draw of a blower motor.
  • ELECTRICAL ACCESSORY SYMPTOM GUIDE
  • Electrical Accessory Symptom Guide
  • Electrical Accessory Symptom Guide
  • Electrical Accessory Symptom Guide
  • Electrical Accessory Symptom Guide
    • NOTE:
      • If the high-speed fuse blows a second time, check the current draw of the motor and replace the blower motor if the current draw is above specifications. Check for possible normal operation if the rear window defogger is not in operation; some vehicles electrically prevent simultaneous operation of the high-speed blower and rear window defogger to help reduce the electrical loads.
  • FREQUENTLY ASKED QUESTION
    • How Do Wipers Park?
      • Some vehicles have wiper arms that park lower than the normal operating position so that they are hidden below the hood when not in operation. This is called a depressed park position.
    ? BACK TO PRESENTATION When the wiper motor is turned off, the park switch allows the motor to continue to turn until the wiper arms reach the bottom edge of the windshield. Then the park switch reverses the current flow through the wiper motor, which makes a partial revolution in the opposite direction. The wiper linkage pulls the wiper arms down below the level of the hood and the park switch is opened, stopping the wiper motor.
  • TECH TIP
    • Use a Scan Tool to Check Accessories
      • Most vehicles built since 2000 can have the lighting and accessory circuits checked using a scan tool. A technician can use the following:
    BACK TO PRESENTATION
    • Factory scan tool, such as:
      • Tech 2 or Multiple Diagnostic Interface (MDI) (General Motors vehicle)
      • DRB III or Star Scan or Star Mobile or WiTech (Chrysler- Jeep vehicles)
      • New Generation Star or IDS (Ford)
      • Honda Diagnostic System (HDS)
      • TIS Tech Stream (Toyota/Lexus)
    • Enhanced aftermarket scan tool that has body bidirectional control capability, including:
      • Snap-on Modis, Solus, or Verus
      • OTC Genisys
      • Autoengenuity
    Using a bidirectional scan tool allows the technician to command the operation of electrical accessories such as windows, lights, and wipers. If the circuit operates correctly when commanded by the scan tool and does not function using the switch(es), follow service information instructions to diagnose the switch circuits.
  • TECH TIP
    • The 20 Ampere Fuse Test
      • Most blower motors operate at about 12 A on high speed. If the bushings (bearings) on the armature of the motor become worn or dry, the motor turns more slowly. Because a motor also produces counterelectromotive force (CEMF) as it spins, a slower-turning motor will actually draw more amperes than a fast-spinning motor.
    BACK TO PRESENTATION
    • If a blower motor draws too many amperes, the resistors or the electronic circuit controlling the blower motor can fail. Testing the actual current draw of the motor is sometimes difficult because the amperage often exceeds the permissible amount for most digital meters.
    • One test recommended by General Motors Co. is to unplug the power lead to the motor (retain the ground on the motor) and use a fused jumper lead with one end connected to the battery’s positive terminal and the other end to the motor terminal. Use a 20 A fuse in the test lead, and operate the motor for several minutes. If the blower motor is drawing more than 20 A, the fuse will blow.
    • Some experts recommend using a 15 A fuse. If the 15 A fuse blows and the 20 A fuse does not, then you know the approximate blower motor current draw.