HVAC Systems - Automatic: Overview Pontiac Aztek I

Test Description

The numbers below refer to the step numbers on the diagnostic table

1. 3. Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
2. 5. Determine if the HVAC Control Module, Body Control Module or Powertrain Control Module have set DTCs which may affect HVAC operation are present.
3. 6. The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.
4. 7. Answer Yes if the first 3 characters of the DTC name begins with B10; regardless of the last 2 characters.

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The numbers below refer to the step numbers on the diagnostic table

1. 3. Tests for the proper operation of the circuit in the high voltage range.
2. 4. Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

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The numbers below refer to the step numbers on the diagnostic table

1. 4. If the pressure signal voltage stays high after disconnecting the pressure sensor electrical connector, the signal circuit is shorted to voltage, or the PCM is faulty.
2. 7. Tests for a high resistance or for an open in the ground circuit.
3. 16. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). Before you replace the PCM, program the new PCM.

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The numbers below refer to the step numbers on the diagnostic table

1. 2. Listen for an audible click when the relay operates. Command the ON and the OFF states. Repeat the commands as necessary.
2. 12. The PCM utilizes Electrically Erasable Programmable Read Only Memory (EEPROM). Program the new PCM before you replace the PCM.

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Important: The following steps must be completed before using the symptom tables.

1. Perform the «DIAGNOSTIC SYSTEM CHECK - HVAC SYSTEMS - AUTOMATIC»(ref-180864-S14171554802005073000000) before using the Symptom Tables in order to verify that all of the following are true: There are no DTCs set. The control modules can communicate via the serial data link.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to: «AIR DELIVERY DESCRIPTION AND OPERATION»(ref-180864-S15570405712005073000000) «AIR TEMPERATURE DESCRIPTION AND OPERATION»(ref-180864-S20457233682005073000000)

The numbers below refer to the step numbers on the diagnostic table

1. 2. The A/C compressor relay output is disabled if engine coolant temperature is above 121°C (250°F). The engine coolant indicator will illuminate at this temperature.
2. 3. Pressing the center of the left side driver temperature control switch and setting the air temperature control switch in a cold setting activates A/C operation. For the purpose of this and future steps where A/C operation is necessary, bi-level mode is used for consistent testing.
3. 6. The HVAC control module is inoperative when the module does not respond to any operator control requests to enable the A/C compressor. The blower motor may still operate independent of the A/C controls.

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The numbers below refer to the step numbers on the diagnostic table

1. 2. This step will determine if one or more blower speeds are inoperative.
2. 3. This step determines if the HVAC control module and blower motor control processor are attempting to control the blower motor speed.
3. 5. The measured voltage on the blower speed control circuit should steadily increase from 0 V to 8.0 V as the blower speed is adjusted from the minimum speed position to the maximum speed position.

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The numbers below refer to the step numbers on the diagnostic table

1. 7. This test is to ensure A/C system is operating normally.
2. 10. The aspirator tube connects to the rear of the HVAC control module. The aspirator tube is used to draw air past the inside air temperature sensor.

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The step numbers below refer to the step numbers on the diagnostic table

1. 3. This checks for A/C compressor clutch always on.
2. 7. This test is to insure cooling system is operating normally.
3. 10. The aspirator tube connects to the rear of the HVAC control module. The aspirator tube is used to draw air past the inside air temperature sensor.

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The numbers below refer to the step numbers on the diagnostic table

1. 3. This step tests for a blower motor that does not operate regardless of the desired blower motor speed.
2. 4. This step tests for a blower motor that operates, yet does not accurately respond to the desired blower motor speed.
3. 5. The HVAC control module is inoperative when the it does not respond to any operator requests. This step verifies that there is power to the HVAC control assembly.
4. 13. The voltage will vary between 0-5 volts during normal operation. The HVAC control assembly connector must be connected during this step.

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1. Remove the I/P cluster trim plate bezel. Refer to «TRIM PLATE BEZEL REPLACEMENT -- INSTRUMENT PANEL (I/P) CLUSTER (AZTEK)»(ref-180879-S00396509732005073000000) or «TRIM PLATE BEZEL REPLACEMENT -- INSTRUMENT PANEL (I/P) CLUSTER (RENDEZVOUS)»(ref-180879-S38776302642005073000000) .
2. Remove the HVAC control module retaining screws.
3. Pull the HVAC control module out from the I/P.
4. Disconnect the aspirator hose (1) from the HVAC control module.
5. Disconnect the electrical connector from the HVAC control module.
6. Remove the HVAC control module.

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1. Connect the electrical connector to the HVAC control module.
2. Connect the aspirator hose (1) to the HVAC control module.
3. Install the HVAC control module to the I/P.
4. Install the HVAC control module retaining screws. Tighten Tighten the screws to 2.5 N.m (22 Ib. in).
5. Install the I/P cluster trim plate bezel. Refer to «TRIM PLATE BEZEL REPLACEMENT -- INSTRUMENT PANEL (I/P) CLUSTER (AZTEK)»(ref-180879-S00396509732005073000000) or «TRIM PLATE BEZEL REPLACEMENT -- INSTRUMENT PANEL (I/P) CLUSTER (RENDEZVOUS)»(ref-180879-S38776302642005073000000) .

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1. Remove the right side I/P insulator. Refer to «CLOSEOUT/INSULATOR PANEL REPLACEMENT -- RIGHT»(ref-180879-S08053438362005073000000) .
2. Disconnect the blower motor electrical connector.
3. Remove the blower motor mounting screws.
4. Remove the blower motor from the HVAC module assembly.
5. Disconnect the electrical connector from the blower motor control processor assembly.
6. Remove the forward blower control processor mounting screws.
7. Remove the rearward blower control processor mounting screw.
8. Remove the blower control processor assembly from the HVAC module assembly.

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1. Install the blower motor control processor assembly to the HVAC module assembly.
2. Install the rearward mounting screw. Tighten Tighten the screw to 1.8 N.m (16 Ib. in).
3. Install the forward mounting screws. Tighten Tighten the screws to 1.8 N.m (16 Ib. in).
4. Connect the electrical connector to the blower control processor assembly.
5. Install the blower motor to the HVAC module assembly.
6. Install the blower motor mounting screws. Tighten Tighten the screws to 1.8 N.m (16 lb ft).
7. Connect the blower motor electrical connector.
8. Install the right side I/P insulator. Refer to «CLOSEOUT/INSULATOR PANEL REPLACEMENT -- RIGHT»(ref-180879-S08053438362005073000000) .

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1. Remove the upper I/P trim pad. Refer to «TRIM PAD REPLACEMENT -- INSTRUMENT PANEL (I/P) UPPER (AZTEK)»(ref-180879-S34715199802005073000000) or «TRIM PAD REPLACEMENT -- INSTRUMENT PANEL (I/P) UPPER (RENDEZVOUS)»(ref-180879-S12000904462005073000000) .
2. Disconnect the recirculation actuator electrical connector.
3. Remove the mounting screws from the recirculation actuator.
4. Remove the recirculation actuator.

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1. Install the recirculation actuator.
2. Install the recirculation actuator mounting screws. Tighten Tighten the screws to 1.6 N.m (14 Ib. in).
3. Connect the recirculation actuator electrical connector.
4. Install the upper I/P trim pad. Refer to «TRIM PAD REPLACEMENT -- INSTRUMENT PANEL (I/P) UPPER (AZTEK)»(ref-180879-S34715199802005073000000) or «TRIM PAD REPLACEMENT -- INSTRUMENT PANEL (I/P) UPPER (RENDEZVOUS)»(ref-180879-S12000904462005073000000) .

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1. Remove the knee bolster from the instrument panel (I/P). Refer to «KNEE BOLSTER REPLACEMENT»(ref-180879-S39023410262005073000000) .
2. Disconnect the mode actuator electrical connector. Important: Count the number of threads showing from the tip of the mode actuator push rod to the end of the retainer clip.
3. Open the mode actuator push rod retainer clip (1) with a small flat-bladed screwdriver.
4. Disconnect the mode actuator push rod (2) from the retainer clip (1). Important: Disconnect the I/P wiring harness clip from the I/P support bracket to help access the mode actuator screws.
5. Disconnect the I/P wiring harness clip from the I/P support bracket.
6. Remove the mode actuator mounting screws.
7. Remove the mode door actuator.

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1. Install the mode actuator.
2. Install the mode actuator mounting screws. Tighten Tighten the screws to 1.6 N.m (14 Ib. in).
3. Connect the I/P wiring harness clip to the I/P support bracket. Important: Align the counted number of threads on the mode actuator push rod (2) with the tip of the retainer clip (1).
4. Connect the mode actuator push rod (2) to the retainer clip (1).
5. Close the push rod retainer clip (1).
6. Connect the mode actuator electrical connector.
7. Install the knee bolster. Refer to «KNEE BOLSTER REPLACEMENT»(ref-180879-S39023410262005073000000) .

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1. Remove the I/P compartment. Refer to «COMPARTMENT REPLACEMENT -- INSTRUMENT PANEL (I/P)»(ref-180879-S07486245002005073000000) .
2. Disconnect and remove the right hand temperature door lever spring (2).
3. Disconnect and remove the right hand temperature lever (1) from the right hand temperature door.
4. Disconnect the right hand temperature actuator electrical connector.
5. Remove the right hand temperature actuator mounting screws.
6. Remove the right hand temperature actuator.

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1. Install the right hand temperature actuator.
2. Install the right hand temperature actuator mounting screws. Tighten Tighten the screws to 1.6 N.m (14 Ib. in).
3. Connect the right hand temperature actuator electrical connector. Important: Align the pin on the right hand air temperature actuator with the slot in the right hand temperature door lever.
4. Install the right hand temperature lever (1) to the right hand temperature door.
5. Connect the right hand temperature door lever spring (2) to the right hand temperature door lever (1) and HVAC module case.
6. Install the I/P compartment. Refer to «COMPARTMENT REPLACEMENT -- INSTRUMENT PANEL (I/P)»(ref-180879-S07486245002005073000000) .

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1. Remove the knee bolster. Refer to «KNEE BOLSTER REPLACEMENT»(ref-180879-S39023410262005073000000) . Important: The HVAC controls must be set to the vent mode to position the defroster door lever for access to the air temperature actuator.
2. Set the HVAC controls to the vent mode to position the defroster door lever.
3. Remove the left hand temperature door lever bolt (3) from the HVAC module.
4. Disconnect and remove the left hand temperature door lever spring (2).
5. Disconnect and remove the left hand temperature door lever (1) from the left hand temperature door.
6. Disconnect the left hand air temperature actuator electrical connector.
7. Remove the left hand air temperature actuator mounting screws.
8. Remove the left hand air temperature actuator.

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1. Install the left hand air temperature actuator.
2. Install the left hand air temperature actuator mounting screws. Tighten Tighten the screws to 1.6 N.m (14 Ib. in).
3. Connect the left hand air temperature actuator electrical connector. Important: Align the pin on the left hand air temperature actuator with the slot in the left hand temperature door lever.
4. Install the left hand temperature door lever (1) to the left hand temperature door.
5. Connect the left hand temperature door lever spring (2) to the left hand temperature door lever (1) and HVAC module case.
6. Install the left hand temperature door lever bolt (3) to the HVAC module case. Tighten Tighten the bolt to 0.9 N.m (8 Ib. in).
7. Install the knee bolster. Refer to «KNEE BOLSTER REPLACEMENT»(ref-180879-S39023410262005073000000) .

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1. Remove the IP carrier. Refer to «INSTRUMENT PANEL (I/P) CARRIER REPLACEMENT»(ref-180879-S34354076872005073000000) .
2. Remove the aspirator hose mounting screw.
3. Disconnect the aspirator hose from the aspirator duct adapter (1).
4. Remove the aspirator hose from the HVAC module.

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1. Install the aspirator hose to the HVAC module.
2. Install the aspirator hose retaining screw. Tighten Tighten the screw 0.9 N.m (8 Ib. in).
3. Connect the aspirator hose to the aspirator duct adapter (1).
4. Install the IP carrier. Refer to «INSTRUMENT PANEL (I/P) CARRIER REPLACEMENT»(ref-180879-S34354076872005073000000) .

Air Delivery Description and Operation

The air delivery description and operation is divided into five areas

1. HVAC Control Components
2. Air Speed
3. Air Delivery
4. Recirculation Operation
5. Automatic Operation

Purge Operation

If the ambient air temperature is less than 2 C (35 F) and the coolant temperature is less than 10 C (50 F), then a 75-second purge will occur. The purge will begin as soon as the coolant temperature reaches 4 C (40 F). The mode door will move to the defrost position and the blower motor will be near half speed.

Recirculation Operation

The HVAC control module controls the air intake through the recirculation actuator. Recirculation is only available when the HVAC control module is in Panel or Bi-level. The recirculation mode will stay on and the recirculation indicator will illuminate until either outside air or a non-recirculation mode is selected. When the recirculation actuator sees an open in the control circuit, the actuator will default to the recirculation position.

Automatic Operation

In automatic operation, the HVAC control module will maintain the comfort level inside of the vehicle by controlling the A/C compressor clutch, the blower motor, the air temperature actuators, mode actuator and recirculation. To place the HVAC system in Automatic mode you must set the temperature and press the drivers temperature knob. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically be adjusted to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature

1. Monitor the following sensors: Inside air temperature sensor Ambient air temperature sensor Sunload sensor
2. Regulate blower motor speed
3. Position the air temperature actuator
4. Position the mode actuator
5. Position the recirculation actuator
6. Request A/C operation

Air Temperature Description and Operation

The air temperature controls are divided in 5 primary areas

1. HVAC Control Components
2. Heating and A/C Operation
3. Automatic Operation
4. Engine Coolant
5. A/C Cycle

Heating and A/C Operation

The purpose of the heating and A/C system is to provide heated and cooled air to the interior of the vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging. The vehicle operator can determine the passenger compartment temperature by adjusting the air temperature switch. Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve the desired temperature

1. Recirculation actuator setting
2. Difference between inside and desired temperature
3. Difference between ambient and desired temperature
4. Blower motor speed setting
5. Mode setting

The control module makes the following actions when automatic operation is not selected, and an air temperature setting is selected

1. When the air temperature switch is placed in the warmest position, the control module commands the air temperature door to divert maximum air past the heater core.
2. When the air temperature switch is placed in the coldest position, the control module commands the air temperature door to direct air to bypass the heater core.
3. When the air temperature switch is placed between the warmest and coldest positions, the control module monitors the following sensor inputs to determine the air temperature door position that diverts the appropriate amount of air through the heater core in order to achieve the desired temperature: Sunload Ambient temperature Inside temperature

The following shows what blower motor, recirculation actuator, and mode actuator adjustments are made for each air temperature switch selection

The A/C system can be engaged by either pressing the driver temperature switch or during automatic operation. The A/C display will illuminate on the HVAC control module display board when the driver temperature switch is pressed. The control module sends a class 2 A/C request message to the powertrain control module (PCM). The HVAC system uses a scroll compressor that incorporates a thermal switch that opens once the compressor temperature is more than 155°C (311°F). The thermal switch is a non-serviceable item. The following conditions must be met in order for the PCM to turn on the compressor clutch

1. HVAC control module Ambient temperature more than 0°C (32°F) Evaporator Temperature more than 2°C (36°F)
2. BCM Battery voltage between 9-16 volts A/C request from the HVAC control module
3. PCM Engine coolant temperature (ECT) is less than 125°C(257°F) Engine RPM is below 5000 RPM A/C Pressure is between 1510-2979 kPa (219-432 psi)

Once engaged, the compressor clutch will be disengaged for the following conditions

1. Compressor thermal switch is opened
2. Throttle position is 100 percent
3. A/C Pressure is more than 2979 kPa (432 psi)
4. A/C Pressure is less than 1510 kPa (219 psi)
5. Engine coolant temperature (ECT) is more than 125°C (257°F)
6. Engine speed is more than 5500 RPM
7. Transmission shift
8. PCM detects excessive torque load
9. PCM detects insufficient idle quality
10. PCM detects a hard launch

When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.

Dual Zone Operation

The HVAC control module uses dual rotary temperature switches. The dual zone controls allows for maximum temperature offset and comfort between the driver and passenger. It is possible to select maximum airflow over the evaporator core with one dual zone switch along with maximum airflow over the heater core with the other dual zone switch. Each air temperature actuator is independent from the other and the passenger side is not limited in it's range of temperature offset.

In automatic operation, the HVAC control module will maintain the comfort level inside of the vehicle by controlling the A/C compressor clutch, the blower motor, the air temperature actuators, mode actuator and recirculation. To place the HVAC system in Automatic mode you must set the temperature and press the drivers temperature knob. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically be adjusted to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature

1. Monitor the following sensors: Inside air temperature sensor Ambient air temperature sensor Sunload sensor
2. Regulate blower motor speed
3. Position the air temperature actuator
4. Position the mode actuator
5. Position the recirculation actuator
6. Request A/C operation