HVAC Systems: Overview Dodge Caravan IV

DESCRIPTION

The A/C compressor clutch assembly consists of a stationary electromagnetic A/C clutch field coil with a zener diode, a pulley bearing and pulley assembly, and a clutch plate. (Scheme 1) These components provide the means to engage and disengage the A/C compressor from the engine accessory drive belt.

The A/C clutch field coil and the pulley bearing and pulley assembly are both retained on the nose of the A/C compressor with snap rings. The clutch plate is splined to the compressor shaft and secured with a bolt.

Scheme 1

OPERATION

The A/C compressor clutch components provide the means to engage and disengage the A/C compressor from the engine accessory drive belt. When the electromagnetic A/C clutch field coil is energized, it magnetically draws the clutch plate into contact with the clutch pulley and drives the compressor shaft. When the coil is not energized, the pulley freewheels on the clutch hub bearing, which is part of the pulley.

A zener diode is connected in parallel with the clutch electromagnetic coil. This diode controls the dissipation of voltage induced into the coil windings by the collapsing of the electromagnetic fields that occurs when the compressor clutch is disengaged. The zener diode dissipates this induced voltage by regulating a current path to ground. This arrangement serves to protect other circuits and components from potentially damaging voltage spikes in the vehicle electrical system that might occur if the voltage induced in the clutch coil windings could not be dissipated.

The compressor clutch engagement is controlled by several components: the A/C-heater control in the passenger compartment, the A/C pressure transducer on the liquid line, the evaporator temperature sensor in the HVAC housing for RS models or on the expansion valve for RG models, the powertrain control module (PCM) in the engine compartment, and the compressor clutch relay in the integrated power module (IPM). The PCM may delay compressor clutch engagement for up to thirty seconds (Refer to ELECTRICAL/ELECTRONIC CONTROL MODULES/POWERTRAIN CONTROL MODULE - DESCRIPTION - PCM OPERATION) .

The A/C compressor clutch components cannot be repaired and, if faulty or damaged, they must be replaced.

The A/C clutch relay is a International Standards Organization (ISO) micro-relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal functions and patterns. The ISO micro-relay terminal functions are the same as a conventional ISO relay. However, the ISO micro-relay terminal pattern (or footprint) is different, the current capacity is lower, and the physical dimensions are smaller than those of the conventional ISO relay. (Scheme 2)

The A/C clutch relay is located in the integrated power module (IPM) in the engine compartment.

Scheme 2

The ISO-standard A/C clutch micro-relay is an electromechanical switch that uses a low current input controlled by the powertrain control module (PCM) to control the high current output to the A/C clutch field coil. The movable, common feed relay contact is held against the fixed, normally closed relay contact by spring pressure. When the electromagnetic relay coil is energized, it draws the movable common feed relay contact away from the fixed, normally closed relay contact and, holds it against the fixed, normally open relay contact. This action allows high current to flow to the A/C clutch field coil.

When the relay coil is de-energized, spring pressure returns the movable relay contact back against the fixed, normally closed contact point. The resistor or diode is connected in parallel with the relay coil, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The A/C clutch relay terminals are connected to the vehicle electrical system through a receptacle in the integrated power module (IPM). The inputs and outputs of the A/C compressor clutch relay include

1. The common feed terminal (30) receives a battery current input from a fuse in the IPM through a fused B(+) circuit at all times.
2. The coil ground terminal (85) receives a ground input from the PCM through the compressor clutch relay control circuit only when the PCM electronically pulls the control circuit to ground.
3. The coil battery terminal (86) receives a battery current input from the PCM through a fused ignition switch output (run-start) circuit only when the ignition switch is in the On or Start positions.
4. The normally open terminal (87) provides a battery current output to the compressor clutch coil through the compressor clutch relay output circuit only when the compressor clutch relay coil is energized.
5. The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the compressor clutch relay coil is de-energized.

The A/C clutch relay cannot be repaired and, if faulty or damaged, it must be replaced. Refer to appropriate SYSTEM WIRING DIAGRAMS article for diagnosis and testing of the ISO-standard micro-relay and for complete HVAC wiring diagrams.

The front A/C-heater control is located at the center of the instrument panel and uses electrical controls. These controls provide the vehicle operator with a number of setting options to help control the climate and comfort within the vehicle.

The front A/C-heater control for the single zone heating-A/C system allows one temperature setting for the entire vehicle, while the dual zone heating-A/C system allows both the driver and the front seat passenger the ability to individually regulate air temperature for their side of the vehicle. All controls are identified by ISO graphic symbols.

The front A/C-heater control module must be recalibrated each time an actuator motor or the A/C-heater control is replaced (Refer to HEATING & AIR CONDITIONING/CONTROLS - FRONT/A/C HEATER CONTROL - STANDARD PROCEDURE -A/C-HEATER CONTROL CALIBRATION) .

The A/C-heater control cannot be repaired. If faulty or damaged, the entire unit must be replaced. The control knobs are available for service replacement.

The A/C pressure transducer is a switch that is installed on a fitting located on the liquid line. An internally threaded hex fitting on the A/C pressure transducer connect it to the externally threaded Schrader-type fitting on the liquid line. A rubber O-ring seals the connection between the A/C pressure transducer and the liquid line fitting. The A/C pressure transducer is connected to the vehicle electrical system by a molded plastic connector with three terminals. (Scheme 3)

Scheme 3

The A/C pressure transducer monitors the pressures in the high side of the refrigerant system through its connection to a fitting on the liquid line. The A/C pressure transducer will change its internal resistance in response to the pressures it monitors. The Schrader-type valve in the liquid line fitting permits the A/C pressure transducer to be removed or installed without disturbing the refrigerant in the system.

The powertrain control module (PCM) provides a five volt reference signal and a sensor ground to the A/C pressure transducer, then monitors the output voltage of the A/C pressure transducer on a sensor return circuit to determine refrigerant pressure. The PCM is programmed to respond to the A/C pressure transducer and other sensor inputs by controlling the operation of the A/C compressor clutch and the radiator cooling fan to help optimize A/C system performance and to protect the system components from damage. The PCM will disengage the A/C compressor clutch when high side pressure rises above 3082 kPa (447 psi) and re-engage the clutch when high side pressure drops below 2937 kPa (426 psi). The A/C pressure transducer will also disengage the A/C compressor clutch if the high side pressure drops below 110 kPa (16 psi) and will re-engage the clutch when the high side pressure rises above 221 kPa (32 psi). If the refrigerant pressure rises above 1655 kPa (240 psi), the PCM will actuate the cooling fan. The A/C pressure transducer input to the PCM will also prevent the A/C compressor clutch from engaging when ambient temperatures are below about 4.5° C (40° F) due to the pressure/temperature relationship of the refrigerant.

The A/C pressure transducer is diagnosed using a DRBIII® scan tool. Refer to POWERTRAIN DIAGNOSTIC PROCEDURES for more information.

The A/C pressure transducer cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The blend door actuators for the front heating-A/C system are reversible, 12-volt Direct Current (DC), servo motors. (Scheme 4) Models with the front single zone heating-A/C system have a single blend-air door, which is controlled by a single blend door actuator. Models with the optional front dual zone heating-A/C system have dual blend-air doors, which are controlled by two blend door actuators.

The blend door actuator for the single zone heating-A/C system is located on the driver side end of the front HVAC air distribution housing, close to the middle of the distribution housing.

For the dual zone heating-A/C system, the same blend door actuator used for the single zone system becomes the driver side blend door actuator, which is mechanically connected to only the driver side blend-air door. A second separate blend door actuator is also located on the driver side of the front HVAC air distribution housing which is mechanically connected to only the passenger side blend-air door.

The front blend door actuators are interchangeable with each other, as well as with the actuators for the mode-air door and the recirculation-air door. Each actuator is contained within an identical black molded plastic housing with an integral wire connector receptacle. Each actuator also has an identical output shaft with splines that connects it to its respective door linkage and two integral mounting tabs that allow the actuator to be secured to the front HVAC housing. The front blend door actuators do not require mechanical indexing to the blend-air doors, as they are electronically calibrated by the A/C-heater control.

The A/C-heater control must be recalibrated each time an actuator motor is replaced (Refer to HEATING & AIR CONDITIONING/CONTROLS - FRONT/A/C HEATER CONTROL - STANDARD PROCEDURE -A/C-HEATER CONTROL CALIBRATION) .

Scheme 4

The blend door actuators are connected to the A/C-heater control through the vehicle electrical system by a dedicated two-wire lead and connector of the HVAC wire harness. The blend door actuator(s) can move the blend-air door(s) in two directions. When the A/C-heater control pulls the voltage on one side of the motor connection high and the other connection low, the blend-air door will move in one direction. When the A/C-heater control reverses the polarity of the voltage to the motor, the blend-air door moves in the opposite direction.

When the A/C-heater control makes the voltage to both connections high or both connections low, the blend-air door stops and will not move.

The A/C-heater control uses a feedback signal positioning system to monitor the operation and relative position of the blend door actuator(s) and the blend-air door(s). The A/C-heater control learns the blend-air door stop positions during the calibration procedure and will store a diagnostic trouble code (DTC) for any problems it detects in the blend door actuator circuits.

The blend door actuators are diagnosed using a DRBIII® scan tool. Refer to POWERTRAIN DIAGNOSTIC PROCEDURES for more information.

The blend door actuators cannot be adjusted or repaired and, if faulty or damaged, they must be replaced.

A front blower motor power module is used on this model when it is equipped with the automatic temperature control (ATC) heating-A/C system. (Scheme 5) Models equipped with the manual temperature control (MTC) heating-A/C system use a blower motor resistor, instead of the blower motor power module (Refer to HEATING & AIR CONDITIONING/CONTROLS-FRONT/RESISTOR-BLOWER MOTOR - DESCRIPTION).

The front blower motor power module is mounted to the rear of the front HVAC housing, directly behind the glove box. The blower motor power module consists of a molded plastic mounting plate with two integral connector receptacles (1). Concealed behind the mounting plate is the power module electronic circuitry and a large finned heat sink (2). The front blower motor power module is accessed for service by removing the glove box.

Scheme 5

The front blower motor power module is connected to the vehicle electrical system through a dedicated lead and connector of the front HVAC wire harness. A second connector receptacle receives the wire harness connector from the front blower motor. The front blower motor power module allows the microprocessor-based automatic temperature control (ATC) A/C-heater control to calculate and provide infinitely variable blower motor speeds based upon either manual blower switch input or the ATC programming using a pulse width modulated (PWM) circuit strategy.

The PWM voltage is applied to a comparator circuit which compares the PWM signal voltage to the front blower motor feedback voltage. The resulting output drives the power module circuitry, which provides a linear output voltage to change or maintain the desired blower speed.

The front blower motor power module is diagnosed using a DRBIII® scan tool. Refer to BODY DIAGNOSTIC PROCEDURES .

The front blower motor power module cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The blower motor relay for the front heating-A/C system is an International Standards Organization (ISO)-type relay. (Scheme 6) Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal functions and patterns.

The front blower motor relay is located in the integrated power module (IPM) in the engine compartment.

Scheme 6

The front blower motor relay is an electromechanical switch that uses a low current input from the front control module (FCM) to control the high current output to the blower motor resistor (manual temperature control) or the blower motor power module (automatic temperature control). The movable, common feed relay contact is held against the fixed, normally closed relay contact by spring pressure. When the electromagnetic relay coil is energized, it draws the movable common feed relay contact away from the fixed, normally closed relay contact and, holds it against the fixed, normally open relay contact. This action allows high current to flow to the blower motor.

When the relay coil is de-energized, spring pressure returns the movable relay contact back against the fixed, normally closed contact point. The resistor or diode is connected in parallel with the relay coil, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The blower motor relay terminals are connected to the vehicle electrical system through a receptacle in the integrated power module (IPM). The inputs and outputs of the blower motor relay include

1. The common feed terminal (30) receives a battery current input from the battery through a B(+) circuit at all times.
2. The coil ground terminal (85) receives a ground input through the front/rear blower motor relay control circuit only when the FCM electronically pulls the control circuit to ground.
3. The coil battery terminal (86) receives a battery current input from the battery through a B(+) circuit at all times.
4. The normally open terminal (87) provides a battery current output to the blower motor resistor (manual temperature control) or blower motor power module (automatic temperature control) through a fuse in the IPM on the fused front blower motor relay output circuit only when the blower motor relay coil is energized.
5. The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the blower motor relay coil is de-energized.

The blower motor relay cannot be repaired and, if faulty or damaged, it must be replaced. Refer to appropriate SYSTEM WIRING DIAGRAMS article for diagnosis and testing of the ISO-standard relay and for complete HVAC wiring diagrams.

A blower motor resistor is used on vehicles equipped with the front manual temperature control (MTC) heating-A/C system. (Scheme 7) Vehicles equipped with the automatic temperature control (ATC) heating-A/C system use a blower motor power module, instead of the blower motor resistor (Refer to HEATING & AIR CONDITIONING/CONTROLS - FRONT/BLOWER MOTOR POWER MODULE - DESCRIPTION).

The front blower motor resistor is mounted to the rear of the front HVAC housing, directly behind the glove box. The front blower motor resistor consists of a molded plastic mounting plate with an integral wire connector receptacle. Concealed behind the mounting plate are coiled resistor wires contained within a ceramic heat sink.

The front blower motor resistor is accessed for service by removing the glove box.

Scheme 7

The front blower motor resistor is connected to the vehicle electrical system through a dedicated wire lead and connector of the front HVAC wire harness. The front blower motor resistor has multiple resistor wires, each of which will reduce the current flow through the front blower motor to change the blower motor speed.

The blower motor control in the manual temperature control system directs the ground path for the front blower motor through the correct resistor wire to obtain the selected speed. With the blower motor control in the lowest speed position, the ground path for the front blower motor is applied through all of the resistor wires. Each higher speed selected with the blower motor control applies the blower motor ground path through fewer of the resistor wires, increasing the blower motor speed.

The front blower motor resistor cannot be adjusted or repaired and, if faulty or damaged (such as a cracked ceramic heat sink), it must be replaced.

The evaporator temperature sensor used for the manual and automatic temperature control systems on RS models is installed on the top of the HVAC housing behind the instrument panel and measures the air temperature downstream of the evaporator. (Scheme 8) The sensor is an electrical thermistor in a plastic housing that is inserted into the HVAC housing. Two terminals within the molded plastic connector receptacle on the sensor connect it to the vehicle electrical system through a take out and connector of the HVAC wire harness.

Scheme 8

The evaporator temperature sensor used for the manual and automatic temperature control systems on RG models is installed on the top of the expansion valve in the right rear corner of the engine compartment and measures the temperature of the evaporator coils. (Scheme 9) The sensor has a small probe that is inserted in a small well in the body of the expansion valve that is filled with a special silicone-based thermal grease. A small molded plastic push-in retainer secures the sensor to a threaded hole in the top surface of the expansion valve. Two terminals within a molded plastic connector receptacle on the sensor connect it to the vehicle electrical system through a take out and connector of the HVAC wire harness.

Scheme 9

The evaporator temperature sensor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The evaporator temperature sensor monitors the temperature of the conditioned air once it passes through the A/C evaporator. The evaporator temperature sensor will change its internal resistance in response to the air temperatures it monitors and is connected to the A/C-heater control through sensor ground and signal circuits. As the conditioned air temperature increases, the resistance of the evaporator temperature sensor decreases and the voltage monitored by the A/C-heater control decreases. The external location of the evaporator temperature sensor allows the sensor to be removed or installed without disturbing the refrigerant in the A/C system.

The A/C-heater control uses this monitored voltage reading as an indication of the evaporator temperature. The A/C-heater control is programmed to respond to this input by sending electronic messages to the powertrain control module (PCM) over the controller area network (CAN) data bus. The PCM then cycles the A/C compressor clutch as necessary to optimize A/C system performance and to protect the A/C system from evaporator freezing.

The evaporator temperature sensor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The evaporator temperature sensor is diagnosed using the DRBIII® scan tool. Refer to BODY DIAGNOSTIC PROCEDURES .

The infrared temperature sensor consists of two infrared transducers that are concealed behind a clear lens located near the top of the instrument panel center bezel. (Scheme 10) These sensors are used only on models equipped with the optional automatic temperature control (ATC) heating-A/C system. A molded plastic connector receptacle on the bottom of the panel outlet unit is concealed behind the center bezel. A short, dedicated jumper wire harness routed behind the center bezel connects the sensors directly to the ATC A/C-heater control module near the bottom of the center bezel. The infrared temperature sensor is integral to the center bezel panel outlet.

Scheme 10

The infrared sensor detects thermal radiation emitted by the driver and front passenger seat occupants and their surroundings and converts its data into a linear pulse width modulated (PWM) output signal which is read by the automatic temperature control (ATC) A/C-heater control. The ATC A/C-heater control uses the infrared sensor data as one of the inputs necessary to automatically control the interior cabin temperature level. By using thermal radiation (surface temperature) measurement, rather than an air temperature measurement, the ATC heating-A/C system is able to adjust itself to the comfort level as perceived by the occupant. This allows the ATC system to compensate for other ambient conditions affecting comfort levels, such as solar heat gain or evaporative heat loss.

The ATC system logic responds to the infrared sensor message by calculating and adjusting the air flow temperature and air flow rate needed to properly obtain and maintain the selected comfort level temperature of the occupants. The A/C-heater control continually monitors the infrared sensor circuits, and will store diagnostic trouble codes (DTCs) for any problem it detects.

The infrared sensor is diagnosed using a DRBIII® scan tool. Refer to BODY DIAGNOSTIC PROCEDURES .

The infrared sensor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The mode door actuator for the front heating-A/C system is a reversible, 12-volt Direct Current (DC), servo motor. see scheme 28 The single mode door actuator is located on the driver side end of the front HVAC air distribution housing, close to the top of the distribution housing. The mode door actuator is mechanically connected to the mode door.

The front mode door actuator is interchangeable with the actuators for the blend-air doors and the recirculation-air door. Each actuator is contained within an identical black molded plastic housing with an integral wire connector receptacle. Each actuator also has an identical output shaft with splines that connects it to its respective door linkage and two integral mounting tabs that allow the actuator to be secured to the front HVAC housing. The front mode door actuator does not require mechanical indexing to the mode-air doors, as it is electronically calibrated by the A/C-heater control.

The A/C-heater control must be recalibrated each time an actuator motor is replaced (Refer to HEATING & AIR CONDITIONING/CONTROLS - FRONT/A/C HEATER CONTROL - STANDARD PROCEDURE -A/C-HEATER CONTROL CALIBRATION) .

The mode door actuator is connected to the A/C-heater control through the vehicle electrical system by a dedicated two-wire lead and connector of the HVAC wire harness. The mode door actuator can move the mode-air doors in two directions. When the A/C-heater control pulls the voltage on one side of the motor connection high and the other connection low, the mode-air doors will move in one direction. When the A/C-heater control reverses the polarity of the voltage to the motor, the mode-air doors move in the opposite direction.

When the A/C-heater control makes the voltage to both connections high or both connections low, the mode-air doors stop and will not move.

The A/C-heater control uses a feedback signal positioning system to monitor the operation and relative position of the mode door actuator and the mode-air doors. The A/C-heater control learns the mode-air doors stop positions during the calibration procedure and will store a diagnostic trouble code (DTC) for any problems it detects in the mode door actuator circuits.

The mode door actuator is diagnosed using a DRBIII® scan tool. Refer to POWERTRAIN DIAGNOSTIC PROCEDURES for more information.

The mode door actuator cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The recirculation door actuator is a reversible, 12 volt direct current (DC), servo motor. see scheme 30 The recirculation door actuator is located on the bottom of the HVAC air inlet housing and is directly connected to the pivot shaft of the recirculation-air door.

The recirculation door actuator is interchangeable with the actuators for the blend-air door(s) and the mode-air doors. Each actuator is contained within an identical black molded plastic housing with an integral wire connector receptacle. Each actuator also has an identical output shaft with splines that connects it to its door linkage and two integral mounting tabs that allow the actuator to be secured to the air inlet housing. The recirculation door actuator does not require mechanical indexing to the recirculation-air door, as it is electronically calibrated by the A/C-heater control.

The A/C-heater control must be recalibrated each time an actuator motor is replaced (Refer to HEATING & AIR CONDITIONING/CONTROLS - FRONT/A/C HEATER CONTROL - STANDARD PROCEDURE -A/C-HEATER CONTROL CALIBRATION) .

The recirculation door actuator is connected to the A/C-heater control through the vehicle electrical system by a dedicated two-wire lead and connector of the HVAC wire harness. The recirculation door actuator can move the recirculation-air door in two directions. When the A/C-heater control pulls the voltage on one side of the motor connection high and the other connection low, the recirculation-air door will move in one direction. When the A/C-heater control reverses the polarity of the voltage to the motor, the recirculation-air door moves in the opposite direction.

When the A/C-heater control makes the voltage to both connections high or both connections low, the recirculation-air door stops and will not move.

The A/C-heater control uses a feedback signal positioning system to monitor the operation and relative position of the recirculation door actuator and the recirculation-air door. The A/C-heater control learns the recirculation-air door stop positions during the calibration procedure and will store a diagnostic trouble code (DTC) for any problems it detects in the recirculation door actuator circuits.

The recirculation door actuator is diagnosed using a DRBIII® scan tool. Refer to POWERTRAIN DIAGNOSTIC PROCEDURES for more information.

The recirculation door actuator cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The rear heating-A/C system is controlled by temperature controls that are centrally mounted directly into the headliner, or if equipped with the available DVD player, located in a housing mounted to the overhead rails. The rear A/C-heater control allows selection of three blower motor speeds and an Off position when the center knob on the front A/C-heater control is set to the Rear position, otherwise the front A/C-heater control operates both front and rear heater-A/C operation.

With the rear A/C-heater control active, temperature selection dictates the air distribution mode (floor or overhead air) of the rear heater-A/C unit. A cool temperature setting directs flow to the overhead outlets and a warm temperature setting to the floor. Refer to BODY DIAGNOSTIC PROCEDURES for further diagnostic information.

Scheme 11

1. Disconnect and isolate the negative battery cable.
2. Using a trim stick C-4755 or equivalent, gently pry the rear A/C-heater control housing off of the overhead rails. (Scheme 11) 1 - REAR A/C-HEATER CONTROL HOUSING 2 - OVERHEAD RAILS 3 - REAR A/C-HEATER CONTROL
3. Remove the rear A/C-heater control and housing assembly from the overhead rails and disconnect the wire harness connector(s) from the back of the control.
4. If required, remove the three screws that secure the rear A/C-heater control to the housing and remove the control from the housing. (Scheme 12)

Scheme 12

Scheme 13

1. Disconnect and isolate the negative battery cable.
2. Using a trim stick C-4755 or equivalent, gently pry the top edge of the control bezel away from the headliner to release the two retaining clips. (Scheme 13)
3. Remove the rear A/C-heater control and bezel assembly from the headliner and disconnect the wire harness connector(s) from the back of the control. 1 - TRIM STICK 2 - BEZEL 3 - REAR A/C-HEATER CONTROL 4 - HEADLINER
4. If required, remove the three screws that secure the rear A/C-heater control to the bezel and remove the control from the bezel. (Scheme 14)

Scheme 14

The rear blend door actuator is a reversible, 12-volt Direct Current (DC), servo motor. see scheme 36 The single blend door actuator for the rear heating-A/C system is located on the outboard side of the rear HVAC housing and is mechanically connected to the blend-air door.

The rear blend door actuator is interchangeable with the actuator for the rear mode-air door. Each actuator is contained within an identical black molded plastic housing with an integral wire connector receptacle. Each actuator also has an identical output shaft with splines that connects it to its respective door linkage and two integral mounting tabs that allow the actuator to be secured to the rear HVAC housing. The blend door actuator does not require mechanical indexing to the blend-air door, as it is electronically calibrated by the A/C-heater control.

The A/C-heater control must be recalibrated each time an actuator motor is replaced (Refer to HEATING & AIR CONDITIONING/CONTROLS - FRONT/A/C HEATER CONTROL - STANDARD PROCEDURE -A/C-HEATER CONTROL CALIBRATION) .

The rear blend door actuator is connected to the front A/C-heater control through the vehicle electrical system by a dedicated two-wire lead and connector of the rear HVAC wire harness. The rear blend door actuator can move the rear blend-air door in two directions. When the front A/C-heater control pulls the voltage on one side of the motor connection high and the other connection low, the rear blend-air door will move in one direction. When the front A/C-heater control reverses the polarity of the voltage to the motor, the rear blend-air door moves in the opposite direction.

When the front A/C-heater control makes the voltage to both connections high or both connections low, the rear blend-air door stops and will not move.

The front A/C-heater control uses a feedback signal positioning system to monitor the operation and relative position of the rear blend door actuator and the blend-air door. The front A/C-heater control learns the rear blend-air door stop positions during the calibration procedure and will store a diagnostic trouble code (DTC) for any problems it detects in the rear blend door actuator circuits.

The rear blend door actuator is diagnosed using a DRBIII® scan tool. Refer to POWERTRAIN DIAGNOSTIC PROCEDURES for more information.

The rear blend door actuator cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The blower motor relay for the rear heating-A/C system is a International Standards Organization (ISO)-type relay. see scheme 38 Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal functions and patterns.

The rear blower motor relay is located in the integrated power module (IPM) in the engine compartment.

The rear blower motor relay is an electromechanical switch that uses a low current input from the front control module (FCM) to control the high current output to the rear blower motor resistor (manual temperature control) or rear blower motor power module (automatic temperature control). The movable, common feed relay contact is held against the fixed, normally closed relay contact by spring pressure. When the electromagnetic relay coil is energized, it draws the movable common feed relay contact away from the fixed, normally closed relay contact and, holds it against the fixed, normally open relay contact. This action allows high current to flow to the rear blower motor.

When the relay coil is de-energized, spring pressure returns the movable relay contact back against the fixed, normally closed contact point. The resistor or diode is connected in parallel with the relay coil, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The rear blower motor relay terminals are connected to the vehicle electrical system through a receptacle in the integrated power module (IPM). The inputs and outputs of the rear blower motor relay include

1. The common feed terminal (30) receives a battery current input from the battery through a B(+) circuit at all times.
2. The coil ground terminal (85) receives a ground input through the front/rear blower motor relay control circuit only when the FCM electronically pulls the control circuit to ground.
3. The coil battery terminal (86) receives a battery current input from the battery through a B(+) circuit at all times.
4. The normally open terminal (87) provides a battery current output to the blower motor resistor (manual temperature control) or blower motor power module (automatic temperature control) through a fuse in the IPM on the fused rear blower motor relay output circuit only when the rear blower motor relay coil is energized.
5. The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the rear blower motor relay coil is de-energized.

Refer to appropriate SYSTEM WIRING DIAGRAMS article for diagnosis and testing of the micro-relay and for complete HVAC wiring diagrams.

A rear blower motor resistor is used on vehicles equipped with the manual temperature control (MTC) heating-A/C system. see scheme 40 Vehicles equipped with the automatic temperature control (ATC) heating-A/C system use a rear blower motor power module, instead of the rear blower motor resistor (Refer to HEATING & AIR CONDITIONING/CONTROLS - REAR/BLOWER MOTOR POWER MODULE - DESCRIPTION).

The rear blower motor resistor is mounted to the rear HVAC housing, directly above the A/C expansion valve. The rear blower motor resistor consists of a molded plastic mounting plate with an integral connector receptacle. Concealed behind the mounting plate is an electrical circuit board with two resistors and a thermal fuse.

The rear blower motor resistor is accessed for service by removing the right quarter and D-pillar trim panels.

The rear blower motor resistor is connected to the vehicle electrical system through a dedicated take out and connector of the rear HVAC wire harness. The rear blower motor resistor has an electrical circuit board with two resistors, each of which will reduce the current flow through the rear blower motor to change the blower motor speed.

The blower motor switch in the manual temperature control system directs the ground path for the rear blower motor through the correct resistor to obtain the selected speed. With the blower motor switch in the lowest speed position, the ground path for the motor is applied through both resistors. Each higher speed selected with the blower motor switch applies the blower motor ground path through fewer of the resistors, increasing the blower motor speed. When the blower motor switch is in the highest speed position, the blower motor resistors are bypassed and the blower motor receives a direct path to ground through the blower motor switch.

The rear blower motor resistor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The mode door actuator for the rear heating-A/C system is a reversible, 12-volt Direct Current (DC), servo motor. see scheme 42 The mode door actuator is located on the outboard side of the rear HVAC housing, above the blend door actuator. The mode door actuator is mechanically connected to the mode door.

The rear mode door actuator is interchangeable with the actuator for the rear blend-air door. Each actuator is contained within an identical black molded plastic housing with an integral wire connector receptacle. Each actuator also has an identical output shaft with splines that connects it to its respective door linkage and two integral mounting tabs that allow the actuator to be secured to the rear HVAC housing. The rear mode door actuator does not require mechanical indexing to the mode-air door, as it is electronically calibrated by the front A/C-heater control.

The A/C-heater control must be recalibrated each time an actuator motor is replaced (Refer to HEATING & AIR CONDITIONING/CONTROLS - FRONT/A/C HEATER CONTROL - STANDARD PROCEDURE -A/C-HEATER CONTROL CALIBRATION) .

The rear mode door actuator is connected to the front heater-A/C control module through the vehicle electrical system by a dedicated two-wire take out and connector of the rear HVAC wire harness. The rear mode door actuator can move the mode door in two directions. When the front heater-A/C control module pulls the voltage on one side of the motor connection high and the other connection low, the rear mode door will move in one direction. When the module reverses the polarity of the voltage to the motor, the rear mode door moves in the opposite direction. When the module makes the voltage to both connections high or both connections low, the mode door stops and will not move. These same motor connections also provide a feedback signal to the front heater-A/C control module. This feedback signal allows the module to monitor the operation and relative positions of the rear mode door actuator and the mode door. The front heater-A/C control module learns the rear mode door stop positions during the calibration procedure and will store a Diagnostic Trouble Code (DTC) for any problems it detects in the mode door actuator circuits.

The rear mode door actuator can be diagnosed using a DRBIII® scan tool. Refer to BODY DIAGNOSTIC PROCEDURES for more information. The rear mode door actuator cannot be adjusted or repaired and, if damaged or faulty, it must be replaced.

A rear blower motor power module is used on this model when it is equipped with the automatic temperature control (ATC) heating-A/C system. see scheme 44 Models equipped with the manual temperature control (MTC) heating-A/C system use a blower motor resistor, instead of the blower motor power module (Refer to HEATING & AIR CONDITIONING/CONTROLS - REAR/BLOWER MOTOR RESISTOR BLOCK - DESCRIPTION).

The rear blower motor power module is installed in the back of the rear HVAC housing, directly above the A/C expansion valve. The power module consists of a molded plastic mounting plate with two integral connector receptacles. Concealed behind the mounting plate is the power module electronic circuitry and a large finned heat sink. The rear blower motor power module is accessed for service by removing the right quarter and D-pillar trim panels.

The rear blower motor power module is connected to the vehicle electrical system through a dedicated lead and connector of the rear HVAC wire harness. A second connector receptacle receives the wire harness connector from the rear blower motor. The rear blower motor power module allows the microprocessor-based automatic temperature control (ATC) A/C-heater control to calculate and provide infinitely variable blower motor speeds based upon either manual blower switch input or the ATC programming using a pulse width modulated (PWM) circuit strategy.

The PWM voltage is applied to a comparator circuit which compares the PWM signal voltage to the rear blower motor feedback voltage. The resulting output drives the power module circuitry, which adjusts the voltage output received from the rear blower motor relay to change or maintain the desired blower speed.

The rear blower motor power module is diagnosed using a DRBIII® scan tool. Refer to BODY DIAGNOSTIC PROCEDURES .

The rear blower motor power module cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

A dust and odor air filter is standard equipment on models equipped with the three zone temperature control systems. (Scheme 15) The filter element is the same size as the front A/C evaporator to ensure ample filtering capacity. A removable door on the bottom of the front HVAC housing below the glove box provides easy access to the filter element for replacement. The filter should be checked and replaced at least once every 24,000 km (15,000 miles) and checked if heater-A/C system performance seems lower than expected.

Scheme 15

The blower motor is a 12-volt, direct current (DC) motor mounted within a plastic housing with a squirrel cage-type blower wheel that is secured to the blower motor shaft and an integral wire harness with a grommet and connector. (Scheme 16) The blower motor and wheel is located in the air inlet housing at the passenger side end of the HVAC housing.

The blower motor can be accessed for service from underneath the instrument panel.

Scheme 16

The front blower motor is used to control the velocity of air moving through the front HVAC housing by spinning the blower wheel within the housing at the selected or programed speed (depending on application).

On models equipped with the manual temperature control (MTC) heating-A/C system, the front blower motor will operate whenever the ignition switch is in the On position and the blower control switch is in any position except Off. On models equipped with the automatic temperature control (ATC) heating-A/C system, the front blower motor will operate whenever the ignition switch is in the On position and the A/C-heater control power is turned on.

The front blower motor relay output circuit is protected by a fuse in the integrated power module (IPM) located in the engine compartment. In the MTC system, the front blower motor speed is controlled by regulating the path to ground through the blower control switch and the blower motor resistor. In the ATC system, the front blower motor speed is controlled by an electronic blower motor power module, which uses a pulse width modulated input from the A/C-heater control and a feedback signal from the blower motor to regulate the blower motor ground path. On both systems, the front blower motor receives battery current whenever the front blower motor relay is energized.

The front blower motor and blower motor wheel are factory balanced and cannot be adjusted or repaired. If faulty or damaged, the front blower motor and blower wheel must be replaced as an assembly.

Note. LHD model shown in illustration. RHD model similar.

All models are equipped with a common HVAC housing assembly that combines A/C and heating capabilities into a single unit mounted within the passenger compartment. (Scheme 17) The HVAC housing assembly consists of three separate housings

1. HVAC housing - The HVAC housing is mounted to the dash panel behind the instrument panel and contains the A/C evaporator and the blower motor resistor or power model (depending on application) and the particulate air filter (if equipped). The HVAC housing consists of a upper and a lower housing that are attached together and has mounting provisions for the air inlet housing, blower motor, air distribution housing and the HVAC wire harness.
2. Air inlet housing - The air inlet housing is mounted to the right end of the HVAC housing and contains the recirculation-air door and actuator.
3. Air distribution housing - The air distribution housing is mounted to the rear of the HVAC housing and contains the heater core, blend-air doors and actuators, mode-air doors and actuator and door linkage.

Scheme 17

The heating-A/C system is a blend-air type system. The blend-air doors control the amount of conditioned air that is allowed to flow through, or around, the heater core. The dual zone heating A/C system uses two blend door actuators.

The A/C system is designed for the use of a non-CFC, R-134a refrigerant and uses an A/C evaporator to cool and dehumidify the incoming air prior to blending it with the heated air. A temperature control determines the discharge air temperature by operating the blend door actuators, which moves the blend-air doors. This allows an almost immediate control of the output air temperature of the system. The mode door actuator operates the mode-air doors which direct the flow of the conditioned air out the various air outlets, depending on the mode selected. The recirculation door actuator operates the recirculation-air door which closes off the fresh air intake and recirculates the air already inside the vehicle. The electric door actuators are connected to the vehicle electrical system by the HVAC wire harness. The blower motor controls the velocity of air flowing through the HVAC housing assembly by spinning the blower wheel within the HVAC housing at the selected speed by use of the blower motor resistor or power model, depending on application.

The air distribution housing must be removed from the HVAC housing and disassembled for service of the mode-air and blend-air doors. The air inlet housing must be removed from HVAC housing and disassembled for service of the recirculation-air door. The HVAC housing must be removed from the vehicle and disassembled for service of the A/C evaporator.

The blower motor for the rear heating-A/C system is a 12-volt, direct current (DC) motor with an integral wire harness and connector that is mounted within a plastic housing with a squirrel cage-type blower wheel, which is secured to the blower motor shaft. (Scheme 18) The blower motor and wheel is located on the outboard side of the rear HVAC housing.

The blower motor can be accessed for service by removing the rear HVAC housing.

Scheme 18

The rear blower motor is used to control the velocity of air moving through the rear HVAC housing by spinning the blower wheel within the housing at the selected or programed speed (depending on application).

On models equipped with the manual temperature control (MTC) heating-A/C system, the rear blower motor will operate only whenever the ignition switch is in the On position, the front blower control switch is in any position except Off and the rear blower control switch on the front A/C-heater control is in any position except Off. On models equipped with the automatic temperature control (ATC) heating-A/C system, the blower motor will operate whenever the ignition switch is in the On position, the A/C-heater control power is turned on and the rear blower control switch on the front A/C-heater control is in any position except Off. The rear blower motor can only be turned off by turning off the rear system at the front A/C-heater control.

The rear blower motor relay output circuit is protected by a fuse in the integrated power module (IPM) located in the engine compartment. In the MTC system, the rear blower motor speed is controlled by regulating the path to ground through the blower control switch and the blower motor resistor. In the ATC system, the rear blower motor speed is controlled by an electronic blower motor power module, which uses a pulse width modulated input from the A/C-heater control and a feedback signal from the rear blower motor to regulate the blower motor ground path. The rear blower motor receives battery current whenever the rear blower motor relay is energized.

The rear blower motor and blower motor wheel are factory balanced and cannot be adjusted or repaired. If faulty or damaged, the rear blower motor and blower wheel must be replaced as an assembly.

The A/C refrigerant lines and hoses are used to carry the refrigerant between the various A/C system components. The refrigerant lines and hoses for the R-134a system on this vehicle consist of a barrier-hose design with a nylon tube sandwiched between rubber layers. The nylon tube helps to contain the R-134a refrigerant, which has a smaller molecular structure than R-12 refrigerant. The ends of the refrigerant lines are made from lightweight aluminum or steel, and commonly use braze-less fittings.

Any kinks or sharp bends in the refrigerant lines and hoses will reduce the capacity of the entire A/C system and can reduce the flow of refrigerant in the system. The radius of all bends in the flexible hose refrigerant lines should be at least ten times the diameter of the hose and the refrigerant lines should be routed so they are at least 80 millimeters (3 inches) away from the exhaust manifold(s) and exhaust pipe(s).

High pressures are produced in the refrigerant system when the A/C compressor is operating. Extreme care must be exercised to make sure that each of the refrigerant system connections is pressure-tight and leak free. It is a good practice to inspect all flexible hose refrigerant lines at least once a year to make sure they are in good condition and properly routed.

The refrigerant lines and hoses are coupled to other A/C system components with block-type fittings. An O-ring seal, or a flat steel gasket with an integral O-ring (dual plane seal), is used to mate the refrigerant line fittings with A/C system components to ensure the integrity of the refrigerant system.

The refrigerant lines and hoses cannot be repaired and, if faulty or damaged, they must be replaced.

The A/C condenser is located in the front of the engine compartment behind the front fascia. The A/C condenser is a heat exchanger that allows the high-pressure refrigerant gas being discharged by the A/C compressor to give up its heat to the air passing over the condenser fins, which causes the refrigerant to cool and change to a liquid state. (Scheme 19)

The A/C condenser may be removed for service without removing the radiator and cooling fan from the vehicle.

The A/C condenser for vehicles equipped with the 2.4L, 3.3L and 3.8L engines are equipped with an integral automatic transmission cooler and tapping block. This design is referred to as a combination cooler.

Scheme 19

When air passes through the fins of the A/C condenser, the high-pressure refrigerant gas within the A/C condenser gives up its heat. The refrigerant then condenses as it leaves the A/C condenser and becomes a high-pressure liquid. The volume of air flowing over the condenser fins is critical to the proper cooling performance of the A/C system. Therefore, it is important that there are no objects placed in front of the radiator grille openings at the front of the vehicle or foreign material on the condenser fins that might obstruct proper air flow. Also, any factory-installed air seals or shrouds must be properly reinstalled following radiator or A/C condenser service.

The A/C condenser cannot be repaired and, if faulty or damaged, it must be replaced.

The A/C evaporator for the front heating-A/C system is located within the front HVAC housing, behind the instrument panel. The front A/C evaporator and insulator are positioned in the front HVAC housing so that all air entering the housing must pass over the evaporator fins before it is distributed through the front heating-A/C system ducts and outlets. However, air passing over the evaporator fins will only be conditioned when the A/C compressor is engaged and circulating refrigerant through the front A/C evaporator. (Scheme 20)

The front A/C evaporator tubes are connected and sealed to the A/C expansion valve by use of rubber O-rings and a tapping block.

The front A/C evaporator can only be serviced by removing and disassembling the front HVAC housing.

Scheme 20

Refrigerant enters the front A/C evaporator from the front A/C expansion valve as a low-temperature, low-pressure mixture of liquid and gas. As air flows over the fins of the front A/C evaporator, the humidity in the air condenses on the fins, and the heat from the air is absorbed by the refrigerant. Heat absorption causes the refrigerant to boil and vaporize. The refrigerant becomes a low-pressure gas when it leaves the front A/C evaporator.

The front A/C evaporator cannot be repaired and, if faulty or damaged, it must be replaced.

The front A/C expansion valve controls the amount of refrigerant entering the front A/C evaporator. The front A/C expansion valve is of a thermostatic expansion valve (TXV) design and consists of an aluminum H-valve type body with an integral thermal sensor. The front A/C expansion valve is located in the engine compartment at the dash panel, between the A/C refrigerant lines and the A/C evaporator. (Scheme 21)

On RG models, the evaporator temperature sensor is installed on the top of the front A/C expansion valve (Refer to HEATING & AIR CONDITIONING/CONTROLS - FRONT/EVAPORATOR TEMPERATURE SENSOR - DESCRIPTION) .

Scheme 21

The A/C expansion valve controls the high-pressure, low temperature liquid refrigerant from the liquid line and converts it into a low-pressure, low-temperature mixture of liquid and gas before it enters the A/C evaporator. A mechanical sensor in the A/C expansion valve monitors the temperature and pressure of the refrigerant leaving the A/C evaporator through the suction line, and adjusts the orifice size at the liquid line port to let the proper amount of refrigerant into the A/C evaporator to meet the vehicle A/C cooling requirements. Controlling the refrigerant flow through the A/C evaporator ensures that none of the refrigerant leaving the A/C evaporator is still in a liquid state, which could damage the A/C compressor.

The A/C expansion valve is a factory calibrated unit and cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The front heater core is mounted into the HVAC air distribution housing, located behind the instrument panel. The heater core is a heat exchanger made of rows of tubes and fins. The heater core tubes are attached to the heater core by a sealing plate and bolt. (Scheme 22)

The heater core can be serviced without removing the air distribution housing from the vehicle.

Scheme 22

Engine coolant is circulated through the heater hoses to the heater core at all times. As the coolant flows through the heater core, heat is removed from the engine and is transferred to the heater core tubes and fins. Air directed through the heater core picks up the heat from the heater core fins. The blend-air door(s) allows control of the heater output air temperature by regulating the amount of air flowing through the heater core. The blower motor speed controls the volume of air flowing through the HVAC housing.

The heater core cannot be repaired and, if faulty or damaged, it must be replaced.

The receiver/drier stores unnecessary refrigerant, filters the refrigerant, helps remove moisture from the refrigerant and retains any refrigerant vapor that may leave the A/C condenser until it becomes a liquid. The receiver/drier is installed on the high-side of the A/C system between the front and rear sections of the A/C liquid line.

The receiver/drier performs a filtering action to prevent foreign material in the refrigerant from contaminating the A/C expansion valve. Refrigerant enters the receiver/drier as a high-pressure, low temperature liquid. Desiccant inside the receiver/drier absorbs any moisture which may have entered and become trapped within the refrigerant system. In addition, during periods of high demand operation of the A/C system, the receiver/drier acts as a reservoir to store surplus refrigerant.

The receiver/drier cannot be repaired. If the receiver/drier is faulty or damaged, or if the refrigerant system has been contaminated or left open to the atmosphere for an indeterminable period or if the A/C compressor has failed, it must be replaced.

The refrigerant used in this air conditioning system is a HydroFluoroCarbon (HFC), type R-134a. Unlike R-12, which is a ChloroFluoroCarbon (CFC), R-134a refrigerant does not contain ozone-depleting chlorine. R-134a refrigerant is a non-toxic, non-flammable, clear, and colorless liquefied gas.

Even though R-134a does not contain chlorine, it must be reclaimed and recycled just like CFC-type refrigerants. This is because R-134a is a greenhouse gas and can contribute to global warming.

R-134a refrigerant is not compatible with R-12 refrigerant in an A/C system. Even a small amount of R-12 refrigerant added to an R-134a refrigerant system will cause A/C compressor failure, refrigerant oil sludge or poor A/C system performance. In addition, the polyalkylene glycol (PAG) synthetic refrigerant oils used in an R-134a refrigerant system are not compatible with the mineral-based refrigerant oils used in an R-12 refrigerant system.

R-134a refrigerant system service ports, service tool couplers and refrigerant dispensing bottles have all been designed with unique fittings to ensure that an R-134a refrigerant system is not accidentally contaminated with the wrong refrigerant (R-12). There are also labels posted in the engine compartment of the vehicle and on the A/C compressor to identify that the A/C system is equipped with R-134a refrigerant.

The refrigerant oil used in R-134a refrigerant systems is a synthetic-based, polyalkylene glycol (PAG), wax-free lubricant. Mineral-based R-12 refrigerant oils are not compatible with PAG oils, and should never be introduced to an R-134a refrigerant system.

There are different PAG oils available, and each contains a different additive package. The Denso 10S17 and 10S20 A/C compressors used in this vehicle are designed to use ND-8 PAG refrigerant oil. Use only this type of refrigerant oil the refrigerant system.

After performing any refrigerant recovery or recycling operation, always replenish the refrigerant system with the same amount of the recommended refrigerant oil as was removed. Too little refrigerant oil can cause A/C compressor damage, and too much can reduce A/C system performance.

PAG refrigerant oil is more hygroscopic than mineral oil, and will absorb any moisture it comes into contact with, even moisture in the air. The PAG oil container should always be kept tightly capped until it is ready to be used. After use, recap the oil container immediately to prevent moisture contamination.

Refrigerant system service ports are used to recover, recycle, evacuate, charge and test the A/C refrigerant system. Unique sizes are used on the two service ports for the R-134a refrigerant system to ensure the system is not accidentally contaminated with R-12 refrigerant or by service equipment used for R-12 refrigerant.

The high side service port is located on the front section of the liquid line near the receiver/drier. The low side service port is located on the A/C suction line near the A/C compressor. The low side A/C service port valve core is serviceable, however, the high side A/C service port valve core is not. If the high side service port valve core is faulty or damaged, the front section of the liquid line will require replacement.

Note. The protective cap aids in service port sealing and helps protects the refrigerant system from contamination. Remember to always reinstall the protective cap onto the service port when refrigerant system service is complete.

Each of the service ports has a threaded plastic protective cap installed over it from the factory. The service port caps are serviceable items.

The A/C evaporator for the rear heating-A/C system is located within the rear HVAC housing, behind the right quarter trim panel. The rear A/C evaporator is positioned in the rear HVAC housing so that all air entering the housing must pass over the evaporator fins before it is distributed through the rear heating-A/C system ducts and outlets. However, air passing over the evaporator fins will only be conditioned when the A/C compressor is engaged and circulating refrigerant through the rear A/C evaporator. (Scheme 23)

The rear A/C evaporator tubes are connected and sealed to the rear A/C expansion valve by use of rubber O-rings and a tapping block.

The rear A/C evaporator can only be serviced by removing and disassembling the rear HVAC housing.

Scheme 23

Refrigerant enters the rear A/C evaporator from the rear A/C expansion valve as a low-temperature, low-pressure mixture of liquid and gas. As air flows over the fins of the rear A/C evaporator, the humidity in the air condenses on the fins, and the heat from the air is absorbed by the refrigerant. Heat absorption causes the refrigerant to boil and vaporize. The refrigerant becomes a low-pressure gas when it leaves the rear A/C evaporator.

The rear A/C evaporator cannot be repaired and, if faulty or damaged, it must be replaced.

The rear "H" valve-type thermal expansion valve (TXV) is located at the rear of the rear HVAC housing between the evaporator line extension and the evaporator coil. High-pressure, low temperature liquid refrigerant from the liquid line passes through the expansion valve orifice, converting it into a low-pressure, low-temperature mixture of liquid and gas before it enters the evaporator coil.

The rear A/C expansion valve controls the high-pressure, low temperature liquid refrigerant from the rear liquid line and converts it into a low-pressure, low-temperature mixture of liquid and gas before it enters the rear A/C evaporator. A mechanical sensor in the rear A/C expansion valve monitors the temperature and pressure of the refrigerant leaving the rear A/C evaporator through the rear suction line, and adjusts the orifice size at the rear liquid line port to let the proper amount of refrigerant into the rear A/C evaporator to meet the vehicle A/C cooling requirements. Controlling the refrigerant flow through the rear A/C evaporator ensures that none of the refrigerant leaving the rear A/C evaporator is still in a liquid state, which could damage the A/C compressor.

For diagnosis and testing of the rear A/C expansion valve, DIAGNOSIS AND TESTING .

The rear A/C expansion valve is factory calibrated and cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The rear heater core is located near the front of the rear HVAC housing, behind the right rear wheel house. It is a heat exchanger made of rows of tubes and fins. One end of the heater core is fitted with a molded plastic tank that includes the mounting provisions for the heater core and connections for the heater core inlet and outlet tubes. (Scheme 24)

The rear heater core can be serviced without removing the rear HVAC housing from the vehicle.

Scheme 24

Engine coolant is circulated through underbody heater hoses to the rear heater core at all times. As the coolant flows through the rear heater core, heat removed from the engine is transferred to the heater core fins and tubes. Air directed through the heater core picks up the heat from the heater core fins. The rear blend-air door allows control of the rear heater output air temperature by controlling how much of the air flowing through the rear HVAC housing is directed through the rear heater core.

The rear heater core cannot be repaired and, if faulty or damaged, it must be replaced.

Underbody lines are used on models equipped with the rear heating-A/C system. (Scheme 25) The underbody suction line, liquid line, and heater tubes can each be serviced separately.

Scheme 25

The rear heating-A/C underbody lines are all serviced as individual components. When disconnecting any line or connection, make sure that the area around the line or connection is clean of any dirt or residue that may enter and contaminate the rear heating-A/C system. see scheme 131and (Scheme 26).

Any kinks or sharp bends in the rear heater-A/C plumbing will reduce the capacity of the entire heating-A/C system. Kinks and sharp bends reduce the system flow. High pressures are produced in the refrigerant system when the A/C compressor is operating. High temperature coolant is present in the heater plumbing when the engine is operating. Extreme care must be exercised to make sure that each of the connections is pressure-tight and leak free.

Scheme 26

Vehicles equipped with the diesel engine are also equipped with a supplemental cabin heater. This cabin heater is mounted under the vehicle and operates similar to an oil fired furnace. The heater burns small amounts of fuel to provide additional heat to the coolant. Coolant is routed from the engine, to the supplemental cabin heater and then to the front heater core. This provides additional heat to the passenger compartment. The supplemental cabin heater system is interfaced to the vehicles on-board computer systems and DRBIII® diagnostics.

The supplemental cabin heater has an electronic control module that monitors the heat output of the heater. The cabin heater operates at full load (5 kW), half load or idle mode (no additional heat) depending on engine coolant temperature.

When ambient temperatures are lower than 15° C (60° F), the supplemental cabin heater automatically operates once each ignition cycle for five minutes. This assures a good fuel supply is always present for the supplemental cabin heater.

The dosing pump is a combined delivery, dosing and shut-off system for the fuel supply to the supplemental cabin heater from the vehicle fuel tank.

The dosing pump is an electrically operated pump that receives its operation instructions from the supplemental cabin heater control module. The pump supplies diesel fuel from the vehicle fuel tank to the cabin heater.

See also:
• POWERTRAIN DIAGNOSTIC PROCEDURES
• BODY DIAGNOSTIC PROCEDURES