HVAC Systems - Automatic Buick Century VI

Fastener Tightening Specifications

HVAC System - Automatic Fastener Tightening Specifications

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Test Description

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

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.

5. Determine if the HVAC Control Module, Body Control Module or Powertrain Control Module have set DTCs which may affect HVAC operation are present.

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.

7. Answer Yes if the first three characters of the DTC name begins with B10; regardless of the last two characters.

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Scan Tool Data List

Use the Scan Tool Data Display Values and Definitions Information in order to assist in diagnosing the HVAC Control Module problems. Compare the vehicles actual scan tool data with the typical data display value table information. Use the data information in order to aid in understanding the nature of the problem when the vehicle does not match with the typical data display values.

The scan tool data values were taken from a known good vehicle under the following conditions

1. The ignition switch is in the ON position.
2. The engine is running at idle.
3. The vehicle is in PARK.
4. The doors are closed.
5. The windows are closed.
6. The A/C is ON.
7. The ambient air temperatures are at 22-27°C (70-80°F).

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Scan Tool Data Definitions

Use the Scan Tool Data Display Values and Definitions Information in order to assist in diagnosing the HVAC Control Module problems. Compare the vehicles actual scan tool data with the typical data display value table information. Use the data information in order to aid in understanding the nature of the problem when the vehicle does not match with the typical data display values.

The scan tool data values were taken from a known good vehicle under the following conditions

1. The ignition switch is in the ON position.
2. The engine is running at idle.
3. The vehicle is in PARK.
4. The doors are closed.
5. The windows are closed.
6. The A/C is ON, in UPPER mode.
7. The ambient air temperatures are at 22-27°C (70-80°F).

The HVAC Scan Tool Data Definitions contains a brief description of all HVAC related parameters available on the scan tool. The list is in alphabetical order. A given parameter may appear in any one of the data lists. In some cases, the parameter may appear more than once or in more than one data list in order to group certain related parameters together.

Heating and Air Conditioning - Data - Desired Blower Mtr Speed: The scan tool displays 0-111 Counts. When the blower motor is OFF, the scan tool displays 0 Counts. When the blower motor controls are placed in the maximum speed setting, the scan tool displays 111 Counts.

Heating and Air Conditioning - Data - Driver Temp Dial: The scan tool displays 15-32°C (59-89°F). The temperature displayed represents the desired system discharge temperature selected by the driver.

Heating and Air Conditioning - Data - Inside Temp Sensor: The scan tool displays 0-5.0 Volts. The voltage displayed represents the inside air temperature sensor signal to the HVAC control module.

Heating and Air Conditioning - Data - LH Mix Mtr Position Feedback: The scan tool displays 0-255 Counts. The counts displayed represent the position of the left air temperature actuator.

Heating and Air Conditioning - Data - LH Mix Mtr Position Requested: The scan tool displays 0-255 Counts. The counts displayed represent the commanded position of the left air temperature actuator.

Heating and Air Conditioning - Data - Mix Motor State: When the left and right air temperature actuators are operating properly, the scan tool displays Normal.

Heating and Air Conditioning - Data - Outside Temp Sensor: The scan tool displays 0-5.0 Volts. The voltage displayed represents the value of the outside air temperature sensor signal.

Heating and Air Conditioning - Data - Passenger Temp Dial: The scan tool displayed represent the position of the PASSENGER temperature dial, 80 being the coolest setting and 176 being the warmest.

Heating and Air Conditioning - Data - Rear Defog Output: The scan tool displays On or Off. When the rear defog button is pressed the scan tool displays On. When the rear defog button is pressed again, the scan tool displays Off.

Heating and Air Conditioning - Data - RH Mix Mtr Position Feedback: The scan tool displays 0-255 Counts. The counts displayed represent the position of the right air temperature actuator.

Heating and Air Conditioning - Data - RH Mix Mtr Position Requested: The scan tool displays 0-226 Counts. The counts displayed represent the commanded position of the right air temperature actuator.

Heating and Air Conditioning - Data - Sun Load Sensor: The scan tool displays 0-5.0 Volts. The voltage displayed represents the value of the sunload sensor signal.

Heating and Air Conditioning - Data - Vacuum Solenoid 1: The scan tool displays On or Off. When Vacuum Solenoid 1 is energized the scan tool displays On. When the solenoid is de-energized the scan tool displays Off.

Heating and Air Conditioning - Data - Vacuum Solenoid 2: The scan tool displays On or Off. When Vacuum Solenoid 2 is energized the scan tool displays On. When the Solenoid is de-energized the scan tool displays Off.

Heating and Air Conditioning - Data - Vacuum Solenoid 3: The scan tool displays On or Off. When Vacuum Solenoid 3 is energized the scan tool displays On. When the solenoid is de-energized the scan tool displays Off.

Heating and Air Conditioning - Data - Vacuum Solenoid 4: The scan tool displays On or Off. When Vacuum Solenoid 4 is energized the scan tool displays On. When the solenoid is de-energized the scan tool displays Off, and the Air Inlet Valve Vacuum Actuator is in the outside air position.

Heating and Air Conditioning - Data - Vacuum Solenoid 5: The scan tool displays On or Off. When Vacuum Solenoid 5 is energized the scan tool displays On. When the solenoid is de-energized the scan tool displays Off.

Heating and Air Conditioning - Inputs - Auto Button: The scan tool displays Off or On. When the AUTO button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Driver Temp Down Button: The scan tool displays Off or On. When the DRIVER TEMP DOWN button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Driver Temp Up Button: The scan tool displays Off or On. When the DRIVER TEMP UP button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Dual Button: The scan tool displays Off or On. When the DUAL button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Fan Down Button: The scan tool displays Off or On. When the BLOWER SPEED CONTROL DOWN button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Fan Up Button: The scan tool displays Off or On. When the BLOWER SPEED CONTROL DOWN button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Front Defrost Button: The scan tool displays Off or On. When the FRONT DEFROST button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Mode Down Button: The scan tool displays Off or On. When the MODE DOWN button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Mode Up Button: The scan tool displays Off or On. When the MODE UP button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Off Button: The scan tool displays Off or On. When the OFF button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Passenger Temp Down Button: The scan tool displays Off or On. When the PASSENGER TEMP DOWN button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Passenger Temp Down Button: The scan tool displays Off or On. When the PASSENGER TEMP UP button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Rear Defrost Button: The scan tool displays Off or On. When the REAR DEFROST button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Recirculate Button: The scan tool displays Off or On. When the RECIRCULATION button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Inputs - Vent Button: The scan tool displays Off or On. When the VENT button is pressed the scan tool displays On. When released, the scan tool displays Off.

Heating and Air Conditioning - Module Information - Calibration ID: The scan tool displays the Calibration ID number for service identification.

Heating and Air Conditioning - Module Information - ROM ID: The scan tool displays the ROM ID number for service identification.

Heating and Air Conditioning - Module Information - ROM Part Number: The scan tool displays the ROM part number for service identification.

PCM - A/C High Side Pressure: The scan tool displays - 103 to +3119 kPa (-14 to +452 psi).

This parameter represents the A/C refrigerant pressure sensor voltage signal converted to pressure.

PCM - A/C High Side Pressure: The scan tool displays 0.00-5.00 Volts. This parameter represents the A/C refrigerant pressure sensor signal.

PCM - A/C Off for WOT: The scan tool displays Yes or No. Yes is displayed when the PCM de-energizes the A/C compressor clutch relay to reduce engine load during wide open throttle.

PCM - A/C Pressure Disable: The scan tool displays Yes or No. Yes is displayed when the system pressure exceeds 2968 kPa (430 psi).

PCM - A/C Relay Circuit Status: The scan tool displays OK or Fault. Fault is displayed when an open or short is detected in the A/C compressor clutch relay ground circuit.

PCM - A/C Relay Command: The scan tool displays ON or OFF. ON is displayed when the PCM has energized the A/C compressor clutch relay.

PCM - A/C Request Signal: The scan tool displays Yes or No. Yes is displayed when the HVAC Control Module is requesting A/C system operation.

PCM - ECT Sensor: The scan tool displays degrees. Scan tool shows the temperature of the ECT Sensor.

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Circuit Description

The following DTCs are for the temperature sensors monitored by the HVAC control module

1. B0332 - ambient air temperature sensor
2. B0333 - ambient air temperature sensor
3. B0337 - inside air temperature sensor
4. B0338 - inside air temperature sensor

The HVAC control module monitors the temperature sensors to maintain the comfort level inside of the vehicle. The temperature sensors are a 2 wire negative temperature co-efficient thermistor. The HVAC control module applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The HVAC control module provides the ground to the air temperature sensors through the low reference circuit. The HVAC control module monitors the voltage drop across the air temperature sensors and uses the inputs for automatic control calculations. When the air temperatures are cold, the resistance of the sensors are high and the voltage signals are high. When the air temperatures are hot, the resistance of the sensors are low and the voltage signals are low. The HVAC control module converts the voltage values to count values where 1 V is approximately equal to 51 counts.

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC

The HVAC control module detects the sensor signal circuit is less than 0.09 volt (5 counts) or more than 4.90 volts (250 counts).

Action Taken When the DTC Sets

1. The HVAC control module uses a default value.
2. The HVAC control module will display - - for ambient air temperature when OFF.

Conditions for Clearing the DTC

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault-free ignition cycles.
3. The DTC can be cleared by using a scan tool.

Diagnostic Aids

If the condition is not present, refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

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

2. The operating range of the sensor is between 0.09-4.90 volts. If the scan tool displays a value between 0-0.08 volt or 4.91-5.0 volts, then the sensor is performing outside of its designed limits.

3. Tests for the proper operation of the circuit in the high voltage range.

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.

5. Tests the signal circuit for a short to ground.

6. Test the signal circuit for a short to voltage, a high resistance, or an open.

7. Tests the low reference circuit for a high resistance or an open.

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The HVAC control module monitors the ambient light on the vehicle through a light sensitive photodiode which is called a sunload sensor. The HVAC control module uses this information to compensate for the effect of the sun on the inside air temperature of the vehicle. When the sunload sensor is in direct sunlight, the signal voltage is low. When the sunload sensor is shaded, the signal voltage is high. The HVAC control module requests A/C compressor clutch engagement and controls the air temperature actuator door positions in order to maintain the selected air temperature.

The ignition is turned ON.

The HVAC control module detects the signal circuit is less than 0.09 V or more than 4.90 V.

The system will default and assume no solar load is present.

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

If condition not present refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

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

2. The operating range of the sensor is between 0.09-4.90 volts. If the scan tool displays a value between 0-0.08 volt or 4.91-5.0 volts, then the sensor is performing outside of its designed limits.

3. Tests for the proper operation of the circuit in the high voltage range.

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 following DTCs are for the HVAC door actuators

1. B0361 - left air temperature actuator
2. B0365 - right air temperature actuator

The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator is a 5 wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5 volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5 volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5 volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts. The HVAC control module converts the voltage values to count values where 1 V is approximately equal to 51 counts. The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

The ignition is turned ON.

The air temperature door position signal circuit stays at or near 0 volts.

No driver warning message will be displayed for this DTC.

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

If the condition is not present, refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

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

3. This step checks for a default action by the actuator. The actuator will default to 128 counts if the air temperature door position circuit is open, shorted to ground, or shorted to voltage. It will also default to this value if the low reference circuit or the 5 volt reference circuit is open.

4. Tests for the air temperature actuator operating within its specified range.

5. Tests the air temperature actuator ground circuit for an open.

6. Tests the air temperature actuator 5 volt reference circuit for a short to ground, short to voltage, or an open.

7. Tests the air temperature door position signal circuit for an open, high resistance, short to ground, or short to voltage.

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The following DTCs are for the HVAC door actuators

1. B0363 - left air temperature actuator
2. B0367 - right air temperature actuator

The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator is a 5 wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5 volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5 volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5 volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts. The HVAC control module converts the voltage values to count values where 1 V is approximately equal to 51 counts. The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

The ignition is turned ON.

The air temperature door signal circuit stays at 4.5 volts or higher.

No driver warning message will be displayed for this DTC.

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

If the condition is not present, refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

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

3. This step checks for a default action by the actuator. The actuator will default to 128 counts if the air temperature door position circuit is open, shorted to ground, or shorted to voltage. It will also default to this value if the low reference circuit or the 5 volt reference circuit is open.

4. Tests for the air temperature actuator operating within its specified range.

5. Tests the air temperature actuator ground circuit for an open.

6. Tests the air temperature actuator 5 volt reference circuit for a short to ground, short to voltage, or an open.

7. Tests the air temperature door position signal circuit for an open, high resistance, short to ground, or short to voltage.

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The following DTCs are for the HVAC door actuators

1. B0441 - Left air temperature actuator
2. B0446 - Right air temperature actuator

The HVAC control module receives an air temperature actuator position signal from the air temperature actuator. The air temperature actuator position sensor is a potentiometer that is tied to a 5 volt reference source. The variable output from the potentiometer feeds back a position signal to a pull-up resistor located in the HVAC control module. This signal is used to determine the necessary drive signal to the air temperature actuator motor to provide the proper air mix door position. This value is stored in the Keep Alive Memory (KAM) portion of the HVAC control module.

When the HVAC control module is first connected to power (or the battery connection is established), the system will perform an actuator calibration routine lasting approximately 60 seconds. During this routine, both right and left air temperature actuators will cycle full travel in both directions learning the end positions. Position feedback readings are sent back to the HVAC control module and compared to a range of acceptable end readings. If during initialization the position feedback readings are not within the acceptable range, a diagnostic code will be set. If the position feedback readings reach values of 0-5 counts or 250-255 counts the HVAC control module will then interpret the reading as a "feedback-short" or "feedback-open" condition respectively.

Conditions for Running DTC

The ignition is in the ON position.

1. A damaged or bound up temperature door mechanism.
2. Improper alignment of the temperature door after air temperature actuator replacement.
3. The air temperature actuator has not been calibrated after replacement.
4. During calibration, the position feedback reading is not within an acceptable range.

No driver warning message will be displayed for this DTC.

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. A history DTC will clear after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

If condition not present refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

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

3. This step checks for a default action by the actuator. The actuator will default to 128 counts if the air temperature door position circuit is open, shorted to ground, or shorted to voltage. It will also default to this value if the low reference circuit or the 5 volt reference circuit is open.

4. Tests for the air temperature actuator operating within its specified range.

5. Tests for the air temperature actuator ignition 3 voltage circuit for an open.

6. Tests the air temperature actuator 5 volt reference circuit for an open

7. Tests the air temperature actuator control circuit for an open, short to ground, or short to voltage.

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The powertrain control module (PCM) monitors the high side refrigerant pressure through a A/C refrigerant pressure sensor. When the pressure is high the signal voltage is high. When the pressure is low the signal voltage is low. When pressure is high the PCM commands the cooling fans on. When pressure is too high or too low the PCM will not allow the A/C compressor clutch to engage. The PCM sends the A/C pressure data to the dash integration module (DIM) over the Class 2 communication line. The DIM will not request A/C compressor clutch engagement if the A/C pressure is too high.

The engine is running.

The A/C refrigerant pressure sensor signal voltage is less than 0.1 V.

OR

The A/C refrigerant pressure sensor signal voltage is more than 4.9 V.

Either of the above conditions are present for more than 20 seconds.

1. The PCM stores the DTC information into memory when the diagnostic runs and fails.
2. The malfunction indicator lamp (MIL) will not illuminate.
3. The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.

1. A History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
2. The current DTC will clear when the diagnostic runs and does not fail.
3. The DTC can be cleared by using a scan tool.

If the condition is not present refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

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

4. Tests for the proper operation of the circuit in the high voltage range.

5. 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.

6. Tests for a short to ground in the 5 volt reference circuit.

8. Tests for a short to voltage, a high resistance, or an open.

15. Perform the recalibration procedure for the powertrain control module.

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The powertrain control module (PCM) monitors the high side refrigerant pressure through a A/C refrigerant pressure sensor. When the pressure is high the signal voltage is high. When the pressure is low the signal voltage is low. When pressure is high the PCM commands the cooling fans on. When pressure is too high or too low the PCM will not allow the A/C compressor clutch to engage. The PCM sends the A/C pressure data to the dash integration module (DIM) over the Class 2 communication line. The DIM will not request A/C compressor clutch engagement if the A/C pressure is too high.

1. The engine is running.
2. The A/C is requested.

The A/C refrigerant pressure sensor signal voltage is less than 0.1 V.

OR

The A/C refrigerant pressure sensor signal voltage is more than 4.9 V.

Either of the above conditions are present for more than 20 seconds.

1. The PCM stores the DTC information into memory when the diagnostic runs and fails.
2. The malfunction indicator lamp (MIL) will not illuminate.
3. The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.

1. A History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
2. The current DTC will clear when the diagnostic runs and does not fail.
3. The DTC can be cleared by using a scan tool.

If the condition is not present refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

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

4. Tests for the proper operation of the circuit in the high voltage range.

5. 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.

6. Tests for a short to ground in the 5 volt reference circuit.

8. Tests for a short to voltage, a high resistance, or an open.

15. Perform the recalibration procedure for the PCM.

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Battery positive voltage is supplied to the A/C compressor clutch relay. The powertrain control module (PCM) controls the relay by grounding the control circuit through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the PCM. When the PCM is commanding a component on, the voltage of the control circuit should be near 0 volts. When the PCM is commanding the control circuit to a component off, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this DTC will set.

The PCM will monitor the control circuit for the following

1. A short to ground
2. A short to voltage
3. An open circuit
4. An open relay coil
5. An internally shorted or excessively low resistance relay coil.

1. The ignition is ON.
2. The ignition voltage is between 9.0 and 18.0 volts.

1. A short to ground, an open circuit, or a short to battery voltage is detected on the control circuit.
2. The condition is present for at least 30 seconds.

1. The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

1. The PCM turns the MIL Off after three consecutive drive trips that the diagnostic runs and does not fail.
2. A last test failed, or the current DTC, clears when the diagnostic runs and does not fail.
3. A History DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction.
4. The DTC can be cleared by using a scan tool.

If the condition is not present refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

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

2. Listen for an audible click when the A/C compressor clutch relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

3. Tests for voltage at the coil side of the A/C compressor clutch relay.

4. Verifies that the PCM is providing ground to the A/C compressor clutch relay.

5. Tests if ground is constantly being applied to the A/C compressor clutch relay.

6. Tests for a short to voltage or an open.

12. Perform the recalibration procedure for the PCM.

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Battery positive voltage is supplied to the A/C compressor clutch relay. The powertrain control module (PCM) controls the relay by grounding the control circuit through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the PCM. When the PCM is commanding a component on, the voltage of the control circuit should be near 0 volts. When the PCM is commanding the control circuit to a component off, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this DTC will set.

The PCM will monitor the control circuit for the following

1. A short to ground
2. A short to voltage
3. An open circuit
4. An open relay coil
5. An internally shorted or excessively low resistance relay coil.

The ignition is ON.

1. A short to ground, an open circuit, or a short to battery voltage is detected on the control circuit.
2. The condition is present for at least 30 seconds.

1. The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns the MIL Off after three consecutive drive trips that the diagnostic runs and does not fail.
2. A last test failed, or the current DTC, clears when the diagnostic runs and does not fail.
3. A History DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction.
4. The DTC can be cleared by using a scan tool.

If the condition is not present refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

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

2. Listen for an audible click when the A/C compressor clutch relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

3. Tests for voltage at the coil side of the A/C compressor clutch relay.

4. Verifies that the PCM is providing ground to the A/C compressor clutch relay.

5. Tests if ground is constantly being applied to the A/C compressor clutch relay.

6. Tests for a short to voltage or an open.

12. Perform the recalibration procedure for the PCM.

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1. Perform the «DIAGNOSTIC SYSTEM CHECK - HVAC SYSTEMS - AUTOMATIC»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic) before using the Symptom Tables in order to verify that all of the following are true: There are no DTCs set. The control module(s) can communicate through 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»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic__air-delivery-description-and-operation) «AIR TEMPERATURE DESCRIPTION AND OPERATION»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic__air-temperature-description-and-operation)

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the HVAC System. Refer to CHECKING AFTERMARKET ACCESSORIES in Wiring Systems.
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Verify the A/C compressor clutch turns freely and is not seized.
4. Verify that the customer is using the correct key to enable personalization and is not inadvertently activating steering wheel or passenger HVAC controls.
5. The A/C compressor will not operate in cold outside air temperatures. Refer to «AIR TEMPERATURE DESCRIPTION AND OPERATION»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic__air-temperature-description-and-operation) .
6. The following conditions may cause window fogging: Wet carpet or mats High humidity Interior water tank Blocked A/C evaporator drain tube Maximum passenger capacity Blocked body pressure relief valves
7. Inspect the air distribution system for causes of reduced air flow: Obstructed or dirty passenger compartment air filter, if equipped Blocked or damaged air inlet or outlet vents

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «HVAC COMPRESSOR CLUTCH DOES NOT ENGAGE»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic)
2. «HVAC COMPRESSOR CLUTCH DOES NOT DISENGAGE»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic)
3. «BLOWER MOTOR ALWAYS ON»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic)
4. «BLOWER MOTOR INOPERATIVE»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic)
5. «BLOWER MOTOR MALFUNCTION»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic)
6. «TOO HOT IN VEHICLE»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic)
7. «TOO COLD IN VEHICLE»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic)
8. «AIR DELIVERY IMPROPER»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic)
9. «AIR RECIRCULATION MALFUNCTION»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic)
10. «VACUUM CONTROL SYSTEM DIAGNOSTIC»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic)
11. LEAK TESTING in Heating, Ventilation and Air Conditioning
12. DEFROSTING INSUFFICIENT in Heating, Ventilation and Air Conditioning
13. NOISE DIAGNOSIS - BLOWER MOTOR in Heating, Ventilation and Air Conditioning
14. NOISE DIAGNOSIS - AIR CONDITIONING (A/C) SYSTEM in Heating, Ventilation and Air Conditioning
15. ODOR DIAGNOSIS in Heating, Ventilation and Air Conditioning

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

2. The A/C compressor relay output is disabled if engine coolant temperature is above 121°C (250°F) for the L36/L67 and 124°C (255°F) for the LG8.

3. Placing the mode switch in any position other than OFF, along with placing 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.

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.

Scheme 427

Scheme 428

Scheme 429

Scheme 430

Scheme 431

Scheme 432

Scheme 433

Scheme 434

Scheme 435

Scheme 436

The number(s) below refer to the step number(s) on the diagnostic table.

2. This step will determine if one or more blower speeds are inoperative.

4. This step determines if the HVAC control module and blower motor control processor are attempting to control the blower motor speed.

6. The measured voltage on the blower motor speed control circuit should steadily decrease from 4.60 V to 1.1 V as the blower motor speed is adjusted from the minimum speed position to the maximum speed position.

Scheme 437

Scheme 438

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

3. This checks for A/C compressor clutch always OFF.

7. This test is to ensure A/C system is operating normally.

Scheme 439

Scheme 440

Scheme 441

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

3. This checks for A/C compressor clutch always ON.

7. This test is to ensure A/C system is operating normally.

Scheme 442

Scheme 443

Scheme 444

The number(s) below refer to the step number(s) on the diagnostic table.

8. Observe the Vacuum Solenoid parameters to verify that the appropriate solenoids are energized for their respective modes. In Vent mode, solenoid 3 is ON. In Defrost mode, solenoids 1 and 3 are ON-Please note that the Defrost switch should be activated in this mode. In Vent/Recirc, solenoids 3 and 4 are ON-Note that the Recirc switch should be activated in this mode. In Heater mode, solenoids 2 and 3 are ON. In Recirc mode solenoids 2, 3, and 4 are ON. In Def/Heater mode, solenoids 2 and 5 are ON.

10. Test the solenoid control circuit of the solenoid that does not click ON and OFF. Verifies that the HVAC control module is providing ground to the solenoid in the vacuum control assembly.

11. Tests if ground is constantly being applied to the vacuum control assembly.

Scheme 445

Scheme 446

The number(s) below refer to the step number(s) on the diagnostic table.

4. Tests for voltage at the vacuum control assembly.

5. Verifies that the HVAC control module is providing ground to the vacuum control assembly.

6. Tests if ground is constantly being applied to the vacuum control assembly.

Scheme 447

Scheme 448

Scheme 449

Scheme 450

Re-Calibrating Actuators

Use the following steps to perform the calibration update

1. Turn OFF the ignition.
2. Remove the battery positive voltage circuit fuse of the HVAC Control Module. IMPORTANT: The module memory will not clear if the battery positive voltage circuit fuse is installed in less than 60 seconds.
3. Wait 60 seconds.
4. Install the fuse.

Scheme 451

Scheme 452

1. Remove the front floor console. Refer to CONSOLE REPLACEMENT - FRONT FLOOR (D06) in Instrument Panel, Gages, and Console.
2. Remove the HVAC control module mounting screws.
3. Disconnect the electrical connector.
4. Remove the HVAC control module.

Installation Procedure

Scheme 453

Scheme 454

1. Connect the electrical connectors.
2. Install the HVAC control module. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
3. Install the HVAC control module mounting screws. Tighten Tighten the screws to 2 N.m (18 lb in).
4. Install the front floor console. Refer to CONSOLE REPLACEMENT - FRONT FLOOR (D06) in Instrument Panel, Gages, and Console. IMPORTANT: Do not adjust any controls on the HVAC control module while the HVAC control module is calibrating. If interrupted improper HVAC performance will result.
5. Start the engine and run for one minute.

Scheme 455

Scheme 456

Scheme 457

1. Remove the right side IP insulator Panel. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - RIGHT in Instrument Panel, Gages and Console.
2. Disconnect the electrical connector from the blower motor control processor.
3. Disconnect the blower motor control processor electrical connector from the blower motor. IMPORTANT: The opening to the blower motor control processor is slotted. Access to the blower motor control processor opening is limited.
4. Loosen both of the forward bolts.
5. Remove the rearward bolt. IMPORTANT: Tilt down the rear of the blower motor control processor.
6. Remove the blower control processor.

Scheme 458

Scheme 459

Scheme 460

1. Install the blower motor control processor. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the blower motor control processor rearward screw. Tighten Tighten the screw to 1.5 N.m (13 lb in).
3. Tighten the blower motor control processor forward screws. Tighten Tighten the screws to 1.5 N.m (13 lb in).
4. Connect the blower motor control processor electrical connector to the blower motor.
5. Connect the electrical connector from the blower motor control processor.
6. Install the right side IP insulator. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - RIGHT in Instrument Panel, Gages and Console.

Scheme 461

1. Remove the instrument panel compartment. Refer to COMPARTMENT REPLACEMENT - INSTRUMENT PANEL (I/P) in Instrument Panel, Gages and Console.
2. Remove the right instrument panel insulator. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - RIGHT in Instrument Panel, Gages and Console.
3. Disconnect the vacuum line from the recirculation actuator.
4. Lift the retaining tab in order to release the recirculation actuator and slide the actuator off of the mounting bracket.
5. Disconnect the vacuum actuator plunger rod from the recirculation lever.
6. Remove the recirculation actuator.

Scheme 462

1. Install the recirculation actuator.
2. Connect the recirculation actuator plunger rod to the recirculation door, then extend the plunger. IMPORTANT: During installation, ensure that the recirculation actuator retaining tab is positioned above the mating base on the HVAC control module case.
3. Push the vacuum actuator toward the HVAC control module case to secure the retaining tab. IMPORTANT: Verify that the vacuum actuator pushrod is not binding on the recirculation lever.
4. Connect the vacuum harness connector to the recirculation actuator.
5. Install the instrument panel compartment. Refer to COMPARTMENT REPLACEMENT - INSTRUMENT PANEL (I/P) in Instrument Panel, Gages and Console.
6. Install the right instrument panel insulator. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - RIGHT in Instrument Panel, Gages and Console.

Scheme 463

Scheme 464

Scheme 465

1. Remove the left instrument panel insulator. Refer to TRIM PAD REPLACEMENT - INSTRUMENT PANEL (I/P) in Instrument Panel, Gages and Console.
2. Remove the instrument panel knee bolster bracket. Refer to KNEE BOLSTER REPLACEMENT in Instrument Panel, Gages and Console.
3. Disconnect the vacuum line from the mode actuator.
4. Lift the lock tab up (1) to remove the actuator.
5. Remove the mode actuator off the slides of the HVAC module assembly.
6. Disconnect the actuator pushrod from the mode door lever and remove the actuator.

Scheme 466

Scheme 467

Scheme 468

1. Connect the actuator pushrod to the mode door lever.
2. Position the actuator on to the slides of the HVAC module assembly.
3. Ensure that the lock tab (1) locks the actuator.
4. Connect the vacuum lines to the mode actuator.
5. Install the instrument panel knee bolster bracket. Refer to KNEE BOLSTER REPLACEMENT in Instrument Panel, Gages and Console.
6. Install the left instrument panel insulator. Refer to TRIM PAD REPLACEMENT - INSTRUMENT PANEL (I/P) in Instrument Panel, Gages and Console.

Scheme 469

1. Remove the right instrument panel insulator panel. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - RIGHT in Instrument Panel, Gages and Console.
2. Remove the I/P compartment. Refer to COMPARTMENT REPLACEMENT - INSTRUMENT PANEL (I/P) in Instrument Panel, Gages, and Console.
3. Disconnect the two vacuum lines from the defroster actuator (3).
4. Disconnect the orange vacuum line from the recirculation actuator and install a hand vacuum pump (2).
5. Remove the defroster actuator from its attachment to the HVAC module case.
6. Using the hand vacuum pump (2) open the recirculation actuator door to the full position.
7. Rotate the defroster actuator to the right and up into the opening between the back of the dash and the opening into the HVAC module.
8. Disconnect the defroster actuator from the defroster door arm.

Scheme 470

1. Install the defroster actuator to the defroster door arm and snap into place on the HVAC module.
2. Connect the vacuum line to the actuator.
3. Remove the hand vacuum pump (2) and reinstall the vacuum line to the recirculation actuator.
4. Install the I/P compartment. Refer to COMPARTMENT REPLACEMENT - INSTRUMENT PANEL (I/P) in Instrument Panel, Gages and Console.
5. Install the right instrument insulator panel. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - RIGHT in Instrument Panel, Gages and Console.

Scheme 471

Scheme 472

1. Remove the right side instrument panel insulator. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - RIGHT in Instrument Panel, Gages and Console.
2. Remove the instrument panel compartment. Refer to COMPARTMENT REPLACEMENT - INSTRUMENT PANEL (I/P) in Instrument Panel, Gages and Console.
3. Disconnect the electrical connector from the right air temperature actuator.
4. Remove the screws which secure the right air temperature actuator.
5. Remove the electric actuator.

Scheme 473

Scheme 474

1. Position the right air temperature actuator, then align the slots in the electric actuator driver to the flats on the shaft.
2. Align the locating hole to the alignment on the HVAC module case.
3. Slide the actuator driver on to the shaft. The actuator driver should seat completely on the shaft and the mounting holes should be flush with the mounting bolts on the HVAC module case. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
4. Install the screws to the right air temperature actuator. Tighten Tighten the screws to 1.5 N.m (13 lb in).
5. Connect the electrical connector to the right air temperature actuator.
6. Install the instrument panel compartment. Refer to COMPARTMENT REPLACEMENT - INSTRUMENT PANEL (I/P) in Instrument Panel, Gages and Console.
7. Install the right side instrument panel insulator. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - RIGHT in Instrument Panel, Gages and Console.
8. Calibrate the actuator. Refer to «RE-CALIBRATING ACTUATORS»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic__re-calibrating-actuators) .

Scheme 475

Scheme 476

1. Remove the left instrument panel insulator. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - LEFT in Instrument Panel, Gages and Console.
2. Remove the knee bolster. Refer to KNEE BOLSTER REPLACEMENT in Instrument Panel, Gages and Console.
3. Disconnect the electrical connector from the left air temperature actuator.
4. Remove the mounting screws from the left air temperature actuator.
5. Remove the left air temperature actuator.

Scheme 477

Scheme 478

1. Position the left air temperature actuator, then align the slots in the electric actuator driver to the flats on the shaft.
2. Align the locating hole to the alignment pin on the HVAC module case.
3. Slide the actuator driver on to the shaft. The actuator driver should set completely on the shaft and the mounting holes should be flush with the mounting bolts on the HVAC module case. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
4. Install the mounting screws to the left air temperature actuator. Tighten Tighten the screws to 1.5 N.m (13 lb in).
5. Connect the electrical connector to the left air temperature actuator.
6. Install the knee bolster. Refer to KNEE BOLSTER REPLACEMENT in Instrument Panel, Gages and Console.
7. Install the left instrument panel insulator. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - LEFT in Instrument Panel, Gages and Console.
8. Calibrate the actuator. Refer to «RE-CALIBRATING ACTUATORS»(/buick/century/vi-1997-2005/remont/automatic-hvac-system/#hvac-systems-automatic__re-calibrating-actuators) .

Scheme 479

Scheme 480

Scheme 481

1. Remove the right side instrument panel insulator. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - RIGHT in Instrument Panel, Gages and Console.
2. Disconnect the electrical connector from the vacuum control assembly.
3. Disconnect the vacuum harness connector from the vacuum control assembly.
4. Remove the mounting screws from the vacuum control assembly. IMPORTANT: Pull the vacuum control assembly straight down to release the tab from the slot in the HVAC module case.
5. Remove the vacuum control assembly.

Scheme 482

Scheme 483

Scheme 484

1. Align the tab to the slot in the HVAC module case, then push up to seat the vacuum control assembly. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the mounting screws to the vacuum control assembly. Tighten Tighten the screws to 1.5 N.m (13 lb in).
3. Connect the vacuum harness connector to the vacuum control assembly.
4. Connect the electrical connector to the vacuum control assembly.
5. Install the right side instrument panel insulator. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - RIGHT in Instrument Panel, Gages and Console.

Scheme 485

Scheme 486

1. Remove the instrument panel insulator. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - RIGHT in Instrument Panel, Gages, and Console.
2. Remove the instrument panel insulator. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - LEFT in Instrument Panel, Gages, and Console.
3. Disconnect the vacuum hoses from the vacuum tank.
4. Remove the screws that secure the vacuum tank to the HVAC module.
5. Remove the vacuum tank.

Scheme 487

Scheme 488

1. Install the vacuum tank to the HVAC control module. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the screws to the vacuum tank. Tighten Tighten the screws to 1.5 N.m (13 lb in).
3. Connect the vacuum hoses to the vacuum tank.
4. Install the instrument panel insulator. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - RIGHT in Instrument Panel, Gages, and Console.
5. Install the instrument panel insulator. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - LEFT in Instrument Panel, Gages, and Console.

Scheme 489

Scheme 490

Scheme 491

Scheme 492

Scheme 493

Scheme 494

Scheme 495

Scheme 496

Scheme 497

Scheme 498

1. Remove the instrument panel trim pad. Refer to TRIM PAD REPLACEMENT - INSTRUMENT PANEL (I/P) in Instrument Panel, Gages and Console.
2. Remove the passenger side SIR inflator module. Refer to Inflatable Restraint Instrument Panel Module Replacement in Air Bag Restraints System.
3. Remove the brake pedal. Refer to Brake Pedal Assembly Replacement in Disc & Drum.
4. Remove the bolts from the steering column support bracket and remove the bracket.
5. Remove the screws from the right and left side air distribution ducts.
6. Remove the air distribution ducts.
7. Remove the bolts from the relay bracket and position the relay bracket aside.
8. Remove the bolts from the BCM bracket and position the BCM bracket aside.
9. Release the wiring harness retaining clips from the cross vehicle beam and position the wiring harness aside.
10. Remove the two screws below the fuse block that hold the main harness connector to the cross vehicle beam.
11. Remove the bolts from the center support bracket of the HVAC module.
12. Remove the center support bracket of the HVAC module.
13. Remove the bolts from the upper support brackets of the HVAC module.
14. Remove the bolts which secure the left cross vehicle beam to the hinge pillar.
15. Remove the bolts which secure the right cross vehicle beam to the hinge pillar.
16. Remove the bolt (1) from the cross vehicle beam.
17. Remove the cross vehicle beam from the vehicle.
18. Remove the retaining screws (1) from the air distribution case cover.
19. Remove the air distribution case cover (2).
20. Pull the aspirator up and out of the HVAC module assembly.
21. Remove the aspirator hose from the aspirator.

Scheme 499

Scheme 500

Scheme 501

Scheme 502

Scheme 503

Scheme 504

Scheme 505

Scheme 506

Scheme 507

Scheme 508

Scheme 509

Scheme 510

1. Install the aspirator hose to the aspirator.
2. Install the aspirator into the case.
3. Install the air distribution case cover (2). NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
4. Install the air distributor cover retaining screws (1). Tighten Tighten the screws to 1.5 N.m (13 lb in).
5. Install the cross vehicle beam to the vehicle.
6. Install the bolts which secure the right cross vehicle beam to the hinge pillar. Tighten the bolts finger tight.
7. Install the bolts which secure the left cross vehicle beam to the hinge pillar. Tighten the bolts finger tight. Tighten Tighten all the bolts to 20 N.m (15 lb ft).
8. Install the bolt (1) to the cross vehicle beam. Tighten Tighten the bolt to 20 N.m (15 lb ft).
9. Install the bolts to the upper support brackets of the HVAC module. Tighten Tighten the bolts to 10 N.m (89 lb in).
10. Install the center support bracket to the HVAC module.
11. Install the bolts to the center support bracket of the HVAC module. Tighten Tighten the bolts to 10 N.m (89 lb in).
12. Install the instrument panel wiring harness on to the cross vehicle beam and secure the retaining clips.
13. Install the two screws below the fuse block that hold the main wire harness connector to the cross vehicle beam.
14. Install the BCM bracket and the bolts. Tighten Tighten the bolts to 10 N.m (89 lb in).
15. Install the relay bracket and the bolts. Tighten Tighten the bolts to 10 N.m (89 lb in).
16. Install the right and left side air distribution duct bolts. Tighten Tighten the bolts to 1.5 N.m (13 lb in).
17. Install the support bracket for the steering column. Tighten Tighten the bolts to 50 N.m (37 lb ft).
18. Install the brake pedal. Refer to Brake Pedal Assembly Replacement in Disc & Drum.
19. Install the passenger side SIR inflator module. Refer to Inflatable Restraint Instrument Panel Module Replacement in Air Bag Restraints System.
20. Install the instrument panel trim pad. Refer to TRIM PAD REPLACEMENT - INSTRUMENT PANEL (I/P) in Instrument Panel, Gages and Console.

Scheme 511

1. Disconnect the electrical connector (1) from the ambient air temperature sensor (3) that is located on the right front radiator air baffle.
2. Remove the push-in retainer (2) from the ambient air temperature sensor.
3. Remove the ambient air temperature sensor (3) from the radiator air baffle.

Scheme 512

1. Align the ambient air temperature sensor (3) to the radiator air baffle.
2. Install the push-in retainer (2) to the ambient air temperature sensor.
3. Connect the electrical connector (1) to the ambient air temperature sensor.
4. Drive the vehicle at a speed of 32 km/h (20 mph) for approximately one and a half minutes or at a speed of 72 km/h (45 mph) for approximately one minute in order to obtain the ambient update.

Scheme 513

1. Remove the instrument panel cluster (IPC) trim plate. Refer to TRIM PLATE BEZEL REPLACEMENT - INSTRUMENT PANEL (I/P) CLUSTER in Instrument Panel, Gages, and Console.
2. Remove the electrical connection at the air temperature sensor.
3. Remove the air temperature sensor from the aspirator hose.

Scheme 514

1. Connect the air temperature sensor to the aspirator hose.
2. Connect the electrical connector for the sensor.
3. Install the IPC trim plate. Refer to TRIM PLATE BEZEL REPLACEMENT - INSTRUMENT PANEL (I/P) CLUSTER in Instrument Panel, Gages and Console.

Scheme 515

1. Remove the instrument panel upper trim pad. Refer to TRIM PANEL REPLACEMENT - INSTRUMENT PANEL (I/P) UPPER in Instrument Panel, Gages and Console.
2. Disconnect the sunload air temperature sensor and the daytime running lamp light sensor from the defroster grille.
3. Disconnect the electrical connector from the sun load air temperature sensor.
4. Remove the sunload sensor.

Scheme 516

1. Connect the electrical connector to the sun load sensor.
2. Install the sun load air temperature sensor and the daytime running lamp light sensor to the defroster grille.
3. Install the instrument panel upper trim pad. Refer to TRIM PANEL REPLACEMENT - INSTRUMENT PANEL (I/P) UPPER in Instrument Panel, Gages and Console.

Air Delivery Description and Operation

The Air Delivery description and operation is divided into 5 areas

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

HVAC Control Module

The HVAC control module is a non-class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The ignition 3 and battery positive voltage circuits provide power to the control module. The control module supports the following features

Scheme 517

Blower Motor Control Processor

The blower motor control processor is an interface between the HVAC control module and the blower motor. The blower motor speed control, battery positive voltage and ground circuits enable the control processor to operate. The HVAC control module provides a PWM signal to the control processor in order to command the blower motor speed. The processor supplies 12 volts to the blower motor through the blower motor voltage supply circuit. The control processor uses the blower motor ground as a low side control to adjust the blower motor speed.

Air Speed

The blower motor forces air to circulate within the vehicle's interior. The vehicle operator determines the blower motor's speed by placing the blower motor switch in a desired speed position or by selecting automatic operation. The blower motor will only operate if the blower motor switch is in any position other than OFF, and the ignition switch is in the RUN position. In manual operation, once a blower speed is selected, the blower speed remains constant until a new speed is selected. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature.

As the requested blower speed increases, the following conditions occur

1. The HVAC control module increases the amount of time that the blower motor speed control circuit is modulated to ground.
2. The voltage and duty cycle, measured between the blower motor speed control circuit and ground, decrease.

As the requested blower speed decreases, the following conditions occur

1. The HVAC control module decreases the amount of time that the blower motor speed control circuit is modulated to ground.
2. The voltage and duty cycle, measured between the blower motor speed control circuit and ground, increase.

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.

Air Distribution

The operator uses the mode switch on the HVAC control module to change the air delivery mode in the vehicle. The HVAC control module communicates the mode door position to the vacuum control assembly through five solenoid control circuits.

Vent Mode

When the operator selects VENT, the mode actuator has vacuum applied to it through the Brown vacuum line, making the vent door open.

Bi-Level Mode

When the operator selects Bi-Level, the following occurs

1. The mode actuator is in neutral position.
2. The defrost actuator has vacuum applied.
3. The defrost actuator closes the defrost door, thus opening the heater door through mechanical linkage.
4. Vacuum is bled off the mode actuator and the vent door is held stationary in the half open position.

Floor Mode

When the operator selects FLOOR, the mode actuator has vacuum applied to it through the Brown vacuum line, pushing the vent door closed. The defrost actuator has vacuum applied to it through the Red vacuum line, pulling the defrost door closed and opening the heater door through mechanical linkage.

Mix-Blend Mode

When the operator selects Mix-Blend, the following occurs

1. The mode actuator has vacuum applied to it through the Red vacuum line, pushing the vent door closed.
2. Vacuum is bled off the defrost actuator, holding the defrost door stationary in the half-open position. The heater door is also held stationary in the half-open position through mechanical linkage.
3. A/C is forced ON.
4. Recirculation is not available.

Defrost Mode

When the operator selects Defrost, the following occurs

1. The mode actuator has vacuum applied to it through the Brown vacuum line, pushing the vent door closed.
2. The defrost actuator has vacuum applied to it through the Yellow vacuum line, pushing the defrost door open and closing the heater door through mechanical linkage.
3. A/C is forced ON.
4. Recirculation is not available.

Recirculation Operation

When the operator presses the Recirculation switch, a solenoid inside the vacuum control assembly connects the recirculation door vacuum actuator to the vacuum source. The recirculation actuator retracts, closing the recirculation door. The recirculation operation can function with blower motor in either the ON or OFF position. Recirculation will continue and the LED will illuminate until either outside air is selected or the next ignition cycle. Recirculation is not available in Defrost and Mix-Blend mode.

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, the following is required

1. The blower motor switch must be in the AUTO position.
2. The air temperature switch must be in any other position other than 66 or 88 degrees.
3. The mode switch must be in the Auto position. 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
4. Monitor the following sensors: Inside air temperature sensor Ambient air temperature sensor Upper air temperature sensor if cool air is required Lower air temperature sensor if warm air is required Sunload sensor
5. Regulate blower motor speed.
6. Position the air temperature actuator.
7. Position the mode actuator.
8. Position the recirculation actuator.
9. Request A/C operation.

Air Temperature Description and Operation

The air temperature controls are divided into 5 areas

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

The HVAC control module is a Class 2 device that interface between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive and ignition 3 voltage circuits provide power to the HVAC control module. The HVAC control module communicates the mode door position to the vacuum control assembly through five solenoid control circuits. The control assembly supports the following features

Scheme 518

Air Temperature Actuator

The actuator is a 5 wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5 volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5 volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5 volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.

The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

Air Temperature Sensors

The air temperature sensor is a 2 wire negative temperature co-efficient thermistor. The vehicle uses the following air temperature sensors

1. Ambient
2. Inside

A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases.

The sensor signal decreases as the resistance decreases. The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts.

The HVAC control module uses the sensor signals to determine the air temperature door position. The air temperature sensor inputs in a dual zone HVAC system are used to adjust the corresponding left and right air temperature door.

If the HVAC control module detects a malfunctioning sensor, then the HVAC control module will set a DTC code. The HVAC control module will substitute a temperature value of 24°C (75°F) if the inside air temperature sensor has a failure. If the ambient air temperature sensor fails, a temperature of 9°C (49°F) will be substituted by the HVAC control module.

The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is corrected. The HVAC control module displays the ambient air temperature value. The ambient air temperature value is displayed or updated under the following conditions

Scheme 519

Sunload Sensor

The sunload sensor is a 2 wire photo diode. Low reference and signal circuits enable the sensor to operate. As the light shining upon the sensor gets brighter, the sensor conductance increases. The sensor signal decreases as the conductance increases. The sensor operates within an intensity range between completely dark and bright. The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts.

The sunload sensor provides the HVAC control module a measurement of the amount of light shining on the vehicle. Bright, or high intensity, light causes the vehicles inside temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle.

If the HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted sunload value. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is fixed.

A/C Refrigerant Pressure Sensor

The A/C refrigerant pressure sensor is a 3 wire piezoelectric pressure transducer. A 5 volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts.

The A/C refrigerant pressure sensor protects the A/C system from operating when an excessively high or low pressure condition exists. The PCM disables the compressor clutch under the following conditions

1. A/C pressure is more than 2826 kPa (410 psi).
2. A/C pressure is less than 207 kPa (30 psi).

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

The control module makes the following actions when an air temperature setting is selected

1. Warmest position - The air temperature door diverts maximum air past the heater core.
2. Coldest position - The air temperature door directs maximum air to bypass the heater core.
3. Between the warmest and coldest positions - The following sensor inputs are monitored to determine the air temperature door position that diverts the appropriate amount of air past the heater core in order to achieve the desired temperature

1. Sunload
2. Ambient temperature
3. Inside temperature

The A/C system can be engaged when the VENT switch is pressed or the HVAC control module is in FRONT DEFROST, MIX-BLEND mode or during automatic operation. The HVAC control module sends a Class 2 A/C request message to the powertrain control module (PCM). The following conditions must be met in order for the PCM to turn on the compressor clutch

1. HVAC control module Ambient temperature is more than 4°C (40°F).
2. PCM

1. Engine coolant temperature (ECT) is less than 124°C (255°F) for the LG8 and 121°C (250°F) for the L36/L67
2. Engine speed is less than 5000 RPM
3. A/C Pressure is between 2826-207 kPa (410-30 psi)

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

1. Throttle position is 100%
2. A/C Pressure is more than 2826 kPa (410 psi)
3. A/C Pressure is less than 207 kPa (30 psi)
4. Engine coolant temperature (ECT) is more than 124°C (255°F) for the LG8 and 121°C (250°F) for the L36/L67
5. Engine speed is more than 5000 RPM
6. Transmission shift
7. PCM detects excessive torque load
8. PCM detects insufficient idle quality
9. PCM detects a hard launch condition

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

Dual Zone Operation

The right air temperature allows the passenger to offset air discharge temperatures on the right side of the vehicle by 3°C (6°F). To activate the dual zone, the passenger pushes the DUAL button so that the indicator light is lit. Press the right arrow button or left arrow button to the desired offset. The switch assembly has LED's that will illuminate in order to inform the passenger of the temperature offset. The temperature offset is allowed as long as the driver's set temperature is not in the maximum hot or cold settings. The display will not show the passenger temperature selection.

The HVAC control module will position the right air temperature actuator, located on the right side of the HVAC module to a position to divert sufficient air past the heater core to achieve the desired passenger temperature.

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, the following is required

1. The blower motor switch must be in the AUTO position.
2. The air temperature switch must be in any other position other than 15°C (60°F) or 32°C (90°F).
3. The mode switch must be in the Auto position. 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
4. Monitor the following sensors: Inside air temperature sensor Ambient air temperature sensor Sunload sensor
5. Regulate blower motor speed.
6. Position the air temperature actuator.
7. Position the mode actuator.
8. Position the recirculation actuator.
9. Request A/C operation.

The automatic HVAC system will warm and cool the vehicle in the most efficient manner. Selecting either the warmest or coldest temperature will not improve the system performance. If the warmest or coldest temperature setting is selected while the HVAC system is in automatic operation, then the following will occur

1. Warmest position - The blower motor speed increases to maximum speed, and the air temperature actuator is placed in the warmest position.
2. Coldest position - The blower motor speed increases to maximum speed. Air temperature actuator is placed in the coldest position. Mode actuator is placed in panel position.

Recirculation actuator is set to the recirculation position.

Engine Coolant

Engine coolant is the key element of the heating system. The thermostat controls engine operating coolant temperature. The thermostat also creates a restriction for the cooling system that promotes a positive coolant flow and helps prevent cavitation. Coolant enters the heater core through the inlet heater hose, in a pressurized state.

The heater core is located inside the HVAC module. The heat of the coolant flowing through the heater core is absorbed by the ambient air drawn through the HVAC module. Heated air is distributed to the passenger compartment, through the HVAC module, for passenger comfort.

The amount of heat delivered to the passenger compartment is controlled by opening or closing the HVAC module air temperature door. The coolant exits the heater core through the return heater hose and recirculated back through the engine cooling system.

A/C Cycle

Refrigerant is the key element in an air conditioning system. R-134a is presently the only EPA approved refrigerant for automotive use. R-134a is an very low temperature gas that can transfer the undesirable heat and moisture from the passenger compartment to the outside air.

The Delphi model V5 A/C compressor is used on this model year vehicle.

The A/C system used on this vehicle is a non-cycling system. Non-cycling A/C systems use a high pressure switch to protect the A/C system from excessive pressure. The high pressure switch will OPEN the electrical signal to the compressor clutch, in the event that the refrigerant pressure becomes excessive. After the high and low side of the A/C system pressure equalize, the high pressure switch will CLOSE. Closing the high pressure switch will complete the electrical circuit to the compressor clutch. The A/C system is also mechanically protected with the use of a high pressure relief valve. If the high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continues to rise, the high pressure relief will pop open and release the refrigerant from the system.

The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat to the refrigerant. The refrigerant is discharged from the compressor through the discharge hose, and forced to flow to the condenser and then through the balance of the A/C system.

Compressed refrigerant enters the condenser in a high temperature, high pressure vapor state. As the refrigerant flows through the condenser, the heat of the refrigerant is transferred to the ambient air passing through the condenser. Cooling the refrigerant causes the refrigerant to condense and change from a vapor to a liquid state.

The condenser is located in front of the radiator for maximum heat transfer. The condenser is made of aluminum tubing and aluminum cooling fins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line to the orifice tube.

The orifice tube is located in the liquid line between the condenser and the evaporator. The orifice tube is the dividing point for the high and the low pressure sides of the A/C system. As the refrigerant passes through the orifice tube, the pressure on the refrigerant is lowered. Due to the pressure differential on the liquid refrigerant, the refrigerant begins to vaporize at the orifice tube. The orifice tube also measures the amount of liquid refrigerant that can flow into the evaporator.

Refrigerant exiting the orifice tube flows into the evaporator core in a low pressure, liquid state. Ambient air is drawn through the HVAC module and passes through the evaporator core. Warm and moist air causes the liquid refrigerant to boil inside the evaporator core. The boiling refrigerant absorbs the moisture and heat from the ambient air. The refrigerant exits the evaporator through the suction line and back to the compressor in a vapor state, completing the A/C cycle of heat removal. At the compressor, the refrigerant is compressed again and the cycle of heat removal is repeated.

The conditioned air is distributed through the HVAC module for passenger comfort. The heat and moisture removed from the passenger compartment also changes form, or condenses, and is discharged from the HVAC module as water.

Scheme 520

See also:
• FASTENER NOTICE
• DIAGNOSTIC SYSTEM CHECK - HVAC SYSTEMS - AUTOMATIC
• AIR DELIVERY DESCRIPTION AND OPERATION
• AIR TEMPERATURE DESCRIPTION AND OPERATION
• RE-CALIBRATING ACTUATORS