Heating & Air Conditioning - Service Information: Overview Dodge Durango III

DESCRIPTION

Four different heating-A/C systems are available on this model.

1. Manual Temperature Control (MTC) Dual Zone
2. Manual Temperature Control (MTC) Tri Zone
3. Automatic Temperature Control (ATC) Dual Zone
4. Automatic Temperature Control (ATC) Tri Zone

To maintain the performance level of the Heating, Ventilation and Air Conditioning (HVAC) system, the engine cooling system must be properly maintained. The use of a bug screen is not recommended. Any obstructions in front of the radiator or A/C condenser will reduce the performance of the A/C and engine cooling systems.

The engine cooling system includes the radiator, thermostat, radiator hoses and the engine coolant pump. See ENGINE COOLING SYSTEM for more information before attempting any service to the engine cooling system.

OPERATION

All the available heating-A/C systems are blend-air type systems. In the front dual zone blend-air heating-A/C systems, two blend-air doors control the amount of conditioned air that is allowed to flow through, or around the heater core. The two blend-air doors provide completely independent side-to-side temperature control of the discharge air. The temperature controls determine the discharge air temperatures by operating the blend door actuators, which move the blend-air doors. This design allows almost immediate control of the output air temperatures. Both of the available rear heating-A/C systems are single zone blend-air systems, with one blend air door.

Scheme 2

Note. Typical blend-air type HVAC system shown in illustration.

The heating-A/C system pulls outside (ambient) air through the fresh air intake (4) located at the cowl panel at the base of the windshield and into the air inlet housing above the Heating, Ventilation and Air Conditioning (HVAC) housing and passes through the A/C evaporator (7). Air flow is then directed either through or around the heater core (2). This is done by adjusting the position of the blend-air door(s) (3) with the temperature control(s) located on the A/C-heater control in the instrument panel. Air flow is then directed out the floor outlet (8), instrument panel outlet (10) or the defroster outlet (1) in various combinations by adjusting the position of the mode-air doors (9 and 11) using the mode control located on the A/C-heater control. The temperature and mode control uses electrical actuators to operate the air doors.

The velocity of the air flow out of the outlets can be adjusted with the blower speed control located on the A/C-heater control.

The fresh air intake can be shut off by pressing the Recirculation button on the A/C-heater control. This will operate the electrically actuated recirculation-air door (5), which closes off the fresh air intake. With the fresh air intake closed, the conditioned air within the vehicle is pulled back into the HVAC housing through the recirculation air intake (6) located within the passenger compartment.

The A/C compressor can be engaged by pressing the A/C (snowflake) button on the Manual Temperature Control (MTC) A/C-heater control or is automatically engaged on the Automatic Temperature Control (ATC) system when set temperatures require conditioned air cooling. On both systems, the A/C compressor will automatically engage when in any Mix to Defrost position. This will remove heat and humidity from the air before it is directed through or around the heater core.

The two slot-type defroster outlets receive airflow from the HVAC housing through the molded plastic defroster ducts, which connect to the HVAC housing defroster outlets. The airflow from the defroster outlets is directed by fixed vanes in the defroster outlet grilles and cannot be adjusted. The defroster outlet grilles are serviceable from the instrument panel top cover.

The side window demister outlets receive airflow from the HVAC housing through the molded plastic demister ducts. The demisters direct air from the HVAC housing through the outlets located on the A-pillars. The airflow from the side window demister outlets is directed by fixed vanes in the demister outlet grilles and cannot be adjusted. The side window demister outlet grilles are not serviceable from the A-pillars. The demisters operate when the controls are in Heat, Bi-level, Mix and Defrost modes.

The four instrument panel outlets receive airflow from the HVAC housing through two molded plastic main panel ducts. One duct directs air flow out of the right side instrument panel outlets, while the other duct delivers air flow to the left side outlets. Each of these outlets can be individually adjusted to direct the flow of air.

The floor outlets receive airflow from the HVAC housing through the floor distribution ducts which are connected to the rear of the HVAC air distribution housing. Two plastic rear distribution ducts and one center console duct attach to the rear of the air distribution housing and provide conditioned air to the rear seating positions. The airflow from the two rear distribution ducts cannot be adjusted. The two outlets located at the rear of the floor console can be individually adjusted to direct the flow of air, but the outlets on either side of the console cannot be adjusted and air flow is directed by fixed vanes.

Note. It is important to keep the HVAC air intake opening clear of debris. Leaf particles and other debris that is small enough to pass through the cowl opening screen can accumulate within the HVAC housing. The closed, warm, damp and dark environment created within the housing is ideal for the growth of certain molds, mildews and other fungi. Any accumulation of decaying plant matter provides an additional food source for fungal spores, which enter the housing with the fresh intake-air. Excess debris, as well as objectionable odors created by decaying plant matter and growing fungi can be discharged into the passenger compartment during heater-A/C operation if the air intake opening is not kept clear of debris.

The front A/C system is designed for the use of non-CFC, R-134a refrigerant and uses an A/C expansion valve to meter the flow of refrigerant to the A/C evaporator. The A/C evaporator cools and dehumidifies the incoming air prior to blending it with the heated air. To maintain minimum evaporator temperatures and prevent evaporator freezing, an evaporator temperature sensor is used. This sensor is located downstream of the evaporator and supplies an evaporator temperature signal to the A/C-heater control.

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(s) stops and will not move. The A/C-heater control uses a pulse-count positioning system to monitor the operation and relative position of the blend door actuators and the blend-air doors. The A/C-heater control learns the blend-air doors 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 actuator(s) is diagnosed using a scan tool. Refer to DIAGNOSIS AND TESTING .

The blend door actuator(s) cannot be adjusted or repaired and must be replaced if inoperative or damaged.

The mode door actuator (1) is a reversible, 12 volt direct current (DC), servo motor. The mode door actuator is located on the upper right side of the HVAC air distribution housing and mechanically connected to the mode-air doors.

The 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 (2). Each actuator has an identical output shaft with splines (3) that connect it to its door linkage and three integral mounting tabs (4) that allow the actuator to be secured to the air distribution housing. The mode door actuator requires mechanical indexing to the mode-air door linkage and is electronically calibrated by the A/C-heater control.

The two mode door actuators are connected to the A/C-heater control through the vehicle electrical system by dedicated two-wire leads and connectors of the HVAC wire harness. The mode door actuators can move the panel/defrost/demist/floor 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 moves in the opposite direction.

When the A/C-heater control makes the voltage to both connections high or both connections low, the mode-air door stops and will not move. The A/C-heater control uses a pulse-count positioning system to monitor the operation and relative position of the mode door actuators 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 actuators are diagnosed using a scan tool. Refer to DIAGNOSIS AND TESTING .

The mode door actuators cannot be adjusted or repaired and must be replaced if inoperative or damaged.

The recirculation door actuator (1) is a reversible, 12 volt direct current (DC), servo motor. The recirculation door actuator is located on 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 doors and the mode-air doors. Each actuator is contained within an identical black molded plastic housing with an integral wire connector receptacle (2). Each actuator has an identical output shaft with splines (3) that connect it to its door linkage and three integral mounting tabs (4) that allow the actuator to be secured to the air inlet housing. The recirculation door actuator requires mechanical indexing to the recirculation door pivot shaft and is electronically calibrated by the A/C-heater control.

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 pulse-count 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 scan tool. Refer to DIAGNOSIS AND TESTING .

The recirculation door actuator cannot be adjusted or repaired and must be replaced if inoperative or damaged.

Note. Automatic Temperature Control (ATC) shown in illustration. Manual Temperature Control (MTC) similar.

Scheme 3

A blower motor power module is used on this model when equipped with either the Automatic Temperature Control (ATC) heating-A/C system, or the Manual Temperature Control (MTC) heating-A/C system.

The blower motor power module is mounted to the passenger side of the HVAC housing, near the blower motor. The blower motor power module consists of a molded plastic housing with mounting plate and two integral connector receptacles (1). Concealed behind the mounting plate is the power module electronic circuitry and a multiple, cylindrical finned, heat sink (2).The blower motor power module is accessed for service from under the instrument panel.

The blower motor power module is connected to the vehicle electrical system through a dedicated lead and connector of the instrument panel wire harness. A second lead and connector of the instrument panel wire harness is connected to the blower motor.

On the Automatic Temperature Control (ATC) system, the blower motor power module allows the microprocessor-based A/C-heater control to calculate and provide infinitely variable blower motor speeds based upon either manual blower switch input or the ATC programming.

On the Manual Temperature Control (ATC) system, the blower motor power module allows the microprocessor-based A/C-heater control to provide an infinite amount of blower motor speeds throughout its operating range, based upon blower switch input.

Both the ATC and MTC systems use a Pulse Width Modulated (PWM) circuit strategy. PWM voltage is applied to a comparator circuit which compares the PWM signal voltage to the 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 blower motor power module is diagnosed using a scan tool. Refer to DIAGNOSIS AND TESTING .

The blower motor power module cannot be adjusted or repaired must be replaced if inoperative or damaged.

The ambient air temperature sensor is a variable resistor that operates on a 5-volt reference signal sent by the Totally Integrated Power Module (TIPM). The ambient air temperature sensor is connected to the TIPM through a two-wire lead and connector of the vehicle wire harness. The ambient air temperature sensor changes its internal resistance in response to changes in the outside air temperature, which either increases or decreases the reference signal voltage read by the TIPM. The TIPM converts and broadcasts the sensor data over the Controller Area Network (CAN) bus, where it is read by the Automatic Temperture Control (ATC) A/C-heater control, Powertrain Control Module (PCM) and other vehicle control modules.

The ambient air temperature sensor is diagnosed using a scan tool. Refer to appropriate powertrain control diagnostic information. .

The ambient air temperature sensor cannot be adjusted or repaired and must be replaced if inoperative or damaged.

Scheme 4

1. Disconnect and isolate the negative battery cable.
2. Remove the grille. Refer to «GRILLE, REMOVAL»(ref-465921-S35029314672012042300000) .
3. Disconnect the wire harness connector (4) from the ambient air temperature sensor (2).
4. Remove the push-pin fastener (1) that secures the ambient air temperature sensor to the condenser/radiator closeout (3) and remove the sensor.

Note. Cutaway view of HVAC housing shown in illustration for clarity.

Scheme 5

The evaporator temperature sensor (1) measures the temperature of the conditioned air downstream of the A/C evaporator (2). The evaporator temperature sensor is an electrical thermistor within a molded plastic case that is inserted into the HVAC housing (3) near the coldest point of the A/C evaporator. Two terminals within the connector receptacle (4) connect the sensor to the vehicle electrical system.

The external location of the evaporator temperature sensor allows the sensor to be removed and installed without disturbing the refrigerant in the A/C system.

The evaporator temperature sensor monitors the temperature of the conditioned air downstream of the A/C evaporator and supplies an input signal to the A/C-heater control. The A/C-heater control uses the evaporator temperature sensor input signal to optimize A/C system performance and to protect the A/C system from evaporator freezing. The evaporator temperature sensor will change its internal resistance in response to the temperatures it monitors and is connected to the A/C-heater control through sensor ground circuit and a 5-volt reference signal circuit. As the temperature of the A/C evaporator decreases, the internal resistance of the evaporator temperature sensor decreases.

The A/C-heater control uses the monitored voltage reading as an indication of evaporator temperature. The A/C-heater control is programmed to respond to this input by requesting the Powertrain Control Module (PCM) to cycle the A/C clutch as necessary to optimize A/C system performance and to protect the A/C system from evaporator freezing.

The evaporator temperature sensor is diagnosed using a scan tool. Refer to DIAGNOSIS AND TESTING .

The evaporator temperature sensor cannot be adjusted or repaired and must be replaced if inoperative or damaged.

Note. Typical sun sensor assembly shown in illustration.

Scheme 6

The Automatic Temperature Control (ATC) heating-A/C system uses a sun sensor (1) to measure sun light intensity. The sun sensor incorporates two sun load sensors (2) within a molded plastic case which is mounted to the instrument panel and a clear lens (3) that protrudes through the defroster grille. The wire harness receptacle (4) connects the sun sensor to the vehicle electrical system.

The ATC heating-A/C system uses two sun sensors to balance the system in response to side-to-side variations in sun light intensity. Passengers in sun and shadow require different functional settings because they experience very different temperatures. The sun sensor assembly provides data to the A/C heater control to help determine proper mode and blend-air door positions and blower motor speeds. The sun sensors are not thermistor type sensors, but rather photo diodes. For this reason the sun sensors responds to sun light intensity rather than temperature. The sun sensor assembly is also used to sense day and night conditions for automatic headlight control on MTC equipped vehicles.

The sun sensor is diagnosed using a scan tool. Refer to DIAGNOSIS AND TESTING .

The sun sensor assembly cannot be adjusted or repaired and must be replaced if inoperative or damaged.

The A/C pressure transducer monitors the pressures in the high side of the A/C refrigerant system through its connection to a fitting on the A/C discharge line, and its internal resistance changes in response to the pressures it monitors. 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 transducer on a sensor return circuit to determine refrigerant pressure. The PCM is programmed to respond to this and other sensor inputs by controlling the operation of the A/C clutch and the radiator cooling fan to help optimize A/C system performance and to protect the A/C system components from damage. The PCM will disengage the A/C clutch when high side pressure rises above 3219 kPa (476 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 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 220 kPa (32 psi). When the refrigerant pressure rises above 1655 kPa (240 psi), the PCM will actuate the cooling fan. The A/C pressure transducer signal to the PCM also prevents the A/C clutch from engaging when ambient temperatures are below about 10° C (50° F), due to the pressure/temperature relationship of the refrigerant.

A Schrader-type valve in the A/C discharge line fitting permits the A/C pressure transducer to be removed or installed without disturbing the refrigerant in the A/C system.

The A/C pressure transducer is diagnosed using a scan tool. Refer to appropriate powertrain control diagnostic information .

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

The rear blend 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 rear heater-A/C wire harness. The rear blend door actuator can move the rear blend-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 rear blend-air door will move in one direction. When the 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 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 A/C-heater control uses a pulse-count positioning system to monitor the operation and relative position of the rear blend door actuator and the rear blend-air door. The 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 circuit.

The rear blend door actuator is diagnosed using a scan tool. Refer to DIAGNOSIS AND TESTING .

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

Scheme 7

1. Disconnect and isolate the negative battery cable.
2. Remove right quarter trim panel. Refer to «PANEL, QUARTER TRIM, REMOVAL»(ref-465921-S07773746672012042300000) .
3. Disconnect the wire harness connector (3) from the rear blend door actuator (4).
4. Remove the three screws (1) that secure the rear blend door actuator to the rear heater-A/C housing (2) and remove the actuator.

Scheme 8

1. Position the rear blend door actuator (1) onto the rear heater-A/C housing (3). If necessary, rotate the actuator slightly to align the splines on the actuator output shaft (4) with those on the blend door coupler (2).
2. Install the three screws (1) that secure the rear blend door actuator (4) to the rear heater-A/C housing (2). Tighten the screws to 2 N.m (17 in. lbs.).
3. Connect the wire harness connector (3) to the rear blend door actuator.
4. Install the right quarter trim panel. Refer to «PANEL, QUARTER TRIM, INSTALLATION»(ref-465921-S22832939962012042300000) .
5. Reconnect the negative battery cable.
6. Calibrate the front and rear A/C systems as follows: Initiate the Actuator Calibration function using a scan tool. Refer to «STANDARD PROCEDURE»(ref-465964-S02140942132012042300000) . Verify that the Actuator Calibration of the front A/C-heater control has passed. Correct any errors before proceeding if the Actuator Calibration has not passed. Rotate the rear temperature control knob counter clockwise to the full cold position. Allow the control to remain in the full cold position for 5 seconds. Rotate the rear temperature control knob clockwise to the full hot position. Allow the control to remain in the full hot position for 5 seconds. Calibration is now complete. Verify proper front and rear heating-A/C system operation.

The rear mode door actuator (1) is a reversible, 12 volt direct current (DC), servo motor. The rear mode door actuator is located on the inboard side of the rear heater-A/C housing. The rear mode door actuator is contained within a black molded plastic housing which has an integral wire connector receptacle (2), three integral mounting tabs (4) and an output shaft with splines (3) that connect the actuator to the rear mode-air door. The rear mode door actuator is interchangeable with the actuator for the blend-air door.

The rear mode door actuator does require mechanical indexing to the rear mode-air door, as it is electronically calibrated by the A/C-heater control.

The rear 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 rear heater-A/C wire harness. The rear mode door actuator can move the rear mode-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 rear mode-air door will move in one direction. When the A/C-heater control reverses the polarity of the voltage to the motor, the rear mode-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 rear mode-air door stops and will not move. The A/C-heater control uses a pulse-count positioning system to monitor the operation and relative position of the rear mode door actuator and the rear mode-air door. The A/C-heater control learns the rear mode-air door stop positions during the calibration procedure and will store a Diagnostic Trouble Code (DTC) for any problems it detects in the rear mode door actuator circuit.

The rear mode door actuator is diagnosed using a scan tool. Refer to DIAGNOSIS AND TESTING .

The rear mode door actuator cannot be adjusted or repaired and must be replaced if inoperative or damaged.

Scheme 9

1. Disconnect and isolate the negative battery cable.
2. Remove right quarter trim panel. Refer to «PANEL, QUARTER TRIM, REMOVAL»(ref-465921-S07773746672012042300000) .
3. Disconnect the wire harness connector (2) from the rear mode door actuator (1).
4. Remove the three screws (4) that secure the rear mode door actuator to the rear heater-A/C housing (3) and remove the actuator.

Scheme 10

1. Position the rear mode door actuator (1) onto the rear heater-A/C housing (4). If necessary, rotate the actuator slightly to align the splines on the actuator output shaft (2) with those in the mode door coupler (3).
2. Install the three screws (4) that secure the rear mode door actuator (1) to the rear heater-A/C housing (3). Tighten the screws to 2 N.m (17 in. lbs.).
3. Connect the wire harness connector (2) to the rear mode door actuator.
4. Install the right quarter trim panel. Refer to «PANEL, QUARTER TRIM, INSTALLATION»(ref-465921-S22832939962012042300000) .
5. Reconnect the negative battery cable.
6. Calibrate the front and rear A/C systems as follows: Initiate the Actuator Calibration function using a scan tool. Refer to «STANDARD PROCEDURE»(ref-465964-S02140942132012042300000) . Verify that the Actuator Calibration of the front A/C-heater control has passed. Correct any errors before proceeding if the Actuator Calibration has not passed. Rotate the rear temperature control knob counter clockwise to the full cold position. Allow the control to remain in the full cold position for 5 seconds. Rotate the rear temperature control knob clockwise to the full hot position. Allow the control to remain in the full hot position for 5 seconds. Calibration is now complete. Verify proper front and rear heating-A/C system operation.

The A/C-heater control for the rear heater-A/C system is mounted in the headliner. The rear control allows intermediate seat passengers to adjust rear temperature and blower motor speed when the front A/C-heater control is set to the Rear position, otherwise the front A/C-heater control operates both the front and the rear heater-A/C systems.

The A/C-heater control for the rear heater-A/C system is a slave potentiometer to the front A/C-heater control.

The rear A/C-heater control is diagnosed using a scan tool. Refer to DIAGNOSIS AND TESTING .

The rear A/C-heater control cannot be repaired and must be replaced if inoperative or damaged.

The rear blower motor power module is connected to the electrical system through a dedicated wire lead and connector of the rear heater-A/C wire harness. A second lead and connector of the rear heater-A/C wire harness is connected to the rear blower motor.

On the Automatic Temperature Control (ATC) system, the rear blower motor power module allows the microprocessor-based A/C-heater control to calculate and provide infinitely variable blower motor speeds based upon either manual blower switch input or the ATC programming.

On the Manual Temperature Control (MTC) system, the rear blower motor power module allows the microprocessor-based A/C-heater control to provide an infinite amount of rear blower motor speeds throughout its operating range, based upon blower switch input.

Both the ATC and MTC systems use a Pulse Width Modulated (PWM) circuit strategy. PWM voltage is applied to a comparator circuit which compares the PWM signal voltage to the blower motor feedback voltage. The resulting output drives the power module circuitry, which provides a linear output voltage to change or maintain the desired rear blower speed.

The rear blower motor power module is diagnosed using a scan tool. Refer to DIAGNOSIS AND TESTING .

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

Scheme 11

1. Disconnect and isolate the negative battery cable.
2. Remove the right quarter trim panel. Refer to «PANEL, QUARTER TRIM, REMOVAL»(ref-465921-S07773746672012042300000) .
3. Disconnect the wire harness connector (4) from the rear blower motor power module (3).
4. Remove the screw (2) that secures the rear blower motor power module to the rear heater-A/C housing (1).
5. Disengage the rear blower motor power module from the rear heater-A/C housing and remove the module.

Note. Typical filter shown.

Scheme 12

Most models are equipped with a particulate air filter (1) that helps purify the outside air entering the HVAC housing. The filter is mounted in the passenger compartment, behind the glove box bin.

The filter should be replaced at least once a year or every 24, 000 km (15, 000 miles) and checked if heating-A/C system performance seems lower than expected. The particulate air filter is labeled with an arrow (2) to indicate the direction of air flow through the filter.

Note. LHD model shown. RHD model similar.

Scheme 13

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. The HVAC housing assembly consists of three separate housings

1. Air inlet housing (1) - The air inlet housing is mounted to the passenger side end of the HVAC housing and contains the recirculation-air door and actuator.
2. HVAC housing (2) - The HVAC housing is mounted behind the instrument panel and contains the A/C evaporator, blower motor resistor block or power model (depending on application) and the blower motor. The HVAC housing consists of a upper and a lower housing that are attached together and has mounting provisions for the air inlet housing and air distribution housing.
3. Air distribution housing (3) - 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, door linkages and the evaporator temperature sensor. When the vehicle is equipped with the 3.0L diesel engine, the air distribution housing also contains the electric Positive Temperature Coefficient (PTC) heater unit.

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 two available dual zone heating A/C systems use 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 two mode door actuators operate 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 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 a blower motor resistor or power model, depending on heater-A/C system application.

The HVAC housing must be removed from the vehicle and disassembled for service of the A/C evaporator. 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 blower motor controls the velocity of air moving through the HVAC housing by spinning the blower wheel within the HVAC air inlet housing at the selected speed.

Both the Manual Temperature Control (MTC) heating-A/C system and the Automatic Temperature Control (ATC) heating-A/C system have an electronic blower motor power module to control blower motor speed. The power module uses a Pulse Width Modulated (PWM) 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 blower motor receives battery current through the Totally Integrated Power Module (TIPM) whenever the ignition switch is in the Run position, and the blower motor control is in any position except Off.

The blower motor control system is diagnosed using a scan tool. Refer to STANDARD PROCEDURE .

The blower motor and blower motor wheel are factory balanced as an assembly and cannot be adjusted or repaired and must be replaced if inoperative or damaged.

Possible causes of an inoperative blower motor include

1. Open fuse
2. Inoperative blower motor power module
3. Inoperative blower motor switch
4. Inoperative mode control switch
5. Inoperative blower motor
6. Inoperative blower motor circuit wiring or wire harness connectors

Models equipped with the rear heating-A/C system are equipped with a common rear heater-A/C housing (1) that combines A/C and heating capabilities into a single unit mounted in the rear of the passenger compartment.

The rear heating-A/C system is a blend-air type system. The rear A/C system is designed for the use of a non-CFC, R-134a refrigerant and uses an A/C expansion valve (6) and an A/C evaporator (5) to cool and dehumidify the incoming air prior to blending it with the heated air. A blend door actuator (8) operates the blend-air door which controls the amount of conditioned air that is allowed to flow through, or around, the heater core (7). The temperature control determines discharge air temperature and moves the blend door actuator. This allows an almost immediate control of the output air temperature of the system. The mode door actuator (9) operates the mode-air door which directs the flow of the conditioned air out the upper or lower air outlets, depending on the discharge air temperature selected. The rear blower motor (2) controls the velocity of air flowing through the rear heater-A/C housing by spinning the blower wheel at the selected or programmed speed by use of the rear blower motor power module (3). All rear electrical components are connected to the vehicle electrical system by the rear heater-A/C wire harness (4).

The rear heater-A/C housing must be removed from the vehicle and disassembled for service of the A/C evaporator, heater core, mode-air door and the blend-air door.

The rear blower motor controls the velocity of the air moving through the rear heater-A/C housing by spinning the blower wheel within the housing at the selected or programmed speed.

The rear blower motor operates only when the ignition switch is in RUN and the front A/C-heater control is set to either front control of rear heating-A/C system, or to the rear control of the rear heating-A/C system. The rear blower motor speed is controlled by the rear blower motor power module.

The rear blower motor and blower wheel are factory balanced and cannot be adjusted or repaired and must be replaced as an assembly if inoperative or damaged.

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.

Note. Replacement of the refrigerant line O-ring seals and gaskets is required anytime a refrigerant line is disconnected. Failure to replace the rubber O-ring seals and metal gaskets could result in a refrigerant system leak.

The A/C condenser has no serviceable parts. The O-ring seals used on the connections are made from a special type of rubber not affected by R-134a refrigerant. The O-ring seals and gaskets must be replaced whenever a refrigerant line is disconnected from the A/C condenser.

The A/C condenser cannot be repaired and must be replaced if leaking or damaged.

Note. LHD model shown. RHD model similar.

Scheme 14

The heater core (1) is mounted into the left side of the HVAC air distribution housing, which is located behind the instrument panel. The heater core is a heat exchanger made of rows of aluminum tubes and fins. The heater core is positioned within the air distribution housing so that only the selected amount of air entering the housing passes through the heater core, before being distributed through the heater-A/C system ducts and outlets. One end of the heater core is fitted with a tank (2) that includes the fittings for the heater core tubes (3)

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

When the engine is running, engine coolant is circulated at all times from the engine through hoses to the heater core. As the coolant flows through the engine and into the heater core, heat is removed from the engine and transferred to the heater core tubes and fins. Air is directed through the heater core and picks up the heat from the heater core fins and tubes and becomes distributed into the HVAC air distribution housing. The blend-air doors allow control of the 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 must be replaced if restricted, leaking or damaged.

The A/C receiver/drier (5) stores unnecessary refrigerant, filters the refrigerant, helps remove moisture from the refrigerant and retains any refrigerant vapor that may leave the A/C condenser (1) until it becomes a liquid. The A/C receiver/drier is on the high-side of the A/C system and is located on the left side of the A/C condenser.

The A/C receiver/drier is integral to the A/C condenser and must be replaced with the condenser as an assembly.

The A/C receiver/drier performs a filtering action to prevent foreign material that may be in the refrigerant from contaminating the A/C expansion valve and the A/C compressor. Refrigerant enters the A/C receiver/drier as a high-pressure, low temperature liquid. Desiccant inside the A/C 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 A/C receiver/drier acts as a reservoir to store surplus refrigerant.

The A/C receiver/drier is integral to the A/C condenser and has no serviceable parts.

The A/C receiver/drier cannot be repaired and the A/C condenser must be replaced if the receiver/drier is leaking or damaged, or if an internal failure of the A/C compressor has occurred. Refer to CONDENSER, A/C, REMOVAL .

Note. LHD model shown. RHD model similar.

Scheme 15

The A/C evaporator (1) for the heating-A/C system is located within the HVAC housing, behind the instrument panel. The A/C evaporator and insulator (2) are positioned in the HVAC housing so that all air entering the housing must pass over the evaporator fins before it is distributed through the 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 A/C evaporator.

The A/C evaporator tubes (4) are connected and sealed to the A/C expansion valve by use of rubber O-rings (5) and a tapping block (3).

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

Refrigerant enters the A/C evaporator from the A/C expansion valve as a low-temperature, low-pressure mixture of liquid and gas. As air flows over the fins of the 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 A/C evaporator.

Note. Replacement of the refrigerant line O-ring seals and gaskets is required anytime a refrigerant line or expansion valve is disconnected. Failure to replace the rubber O-ring seals and metal gaskets could result in a refrigerant system leak.

The A/C evaporator has no serviceable parts except for the O-ring seals. The O-ring seals used on the connections are made from a special type of rubber not affected by R-134a refrigerant. The O-ring seals must be replaced whenever the A/C expansion valve is removed from the A/C evaporator.

The A/C evaporator cannot be repaired and must be replaced if leaking or damaged.

The A/C expansion valve controls the high-pressure, low temperature liquid refrigerant from the A/C 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 A/C suction line, and adjusts the orifice size at the liquid line port to let the proper amount of refrigerant into the 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.

Note. Replacement of the refrigerant line O-ring seals is required anytime a refrigerant line is disconnected from the expansion valve. Failure to replace the rubber O-ring seals could result in a refrigerant system leak.

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

Engine coolant is circulated through heater hoses and tubes to the rear heater core at all times. As the coolant flows through the heater core, heat removed from the engine is transferred to the heater core fins and the air directed through the heater core picks up the heat from the fins. The rear blend air door allows control of the rear heater output air temperature by controlling the amount of air flowing through or around the rear heater core. The rear blower motor speed controls the volume of air flowing through the rear heater-A/C housing.

The rear heater core cannot be repaired and must be replaced if inoperative, leaking or damaged.

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.

Note. Replacement of the refrigerant line O-ring seals and gaskets is required anytime a refrigerant line or expansion valve is disconnected. Failure to replace the rubber O-ring seals and metal gaskets could result in a refrigerant system leak.

The A/C evaporator has no serviceable parts except for the O-ring seals. The O-ring seals used on the connections are made from a special type of rubber not affected by R-134a refrigerant. The O-ring seals must be replaced whenever the rear A/C expansion valve is removed from the rear A/C evaporator.

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

The rear A/C expansion valve controls the flow of high-pressure, low temperature liquid refrigerant entering the expansion valve and converts it into a low-pressure, low-temperature mixture of liquid and gas before it enters the rear A/C evaporator. To meet the vehicles A/C cooling requirements, a mechanical sensor is used in the rear A/C expansion valve to monitor the temperature and pressure of the refrigerant leaving the rear A/C evaporator and then adjust the inlet port orifice size to allow only the proper amount of refrigerant to enter the evaporator. Controlling the refrigerant flow through the rear A/C evaporator ensures that none of the refrigerant leaving the evaporator is still in a liquid state, which could damage the A/C compressor.

Note. Replacement of the refrigerant line O-ring seals and gaskets is required anytime a refrigerant line or expansion valve is disconnected. Failure to replace the rubber O-ring seals and metal gaskets may result in a refrigerant system leak.

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