HVAC Systems - Manual Buick Century VI

Fastener Tightening Specifications

HVAC Systems - Manual 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.

4. Determine if the Powertrain Control Module have set DTCs which may affect HVAC operation are present.

5. The presence of DTCs which begin with "U" indicates some other module is not communicating. The specified procedure will compile all the available information before tests are performed.

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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 temperature are at 22-27°C (70-80°F).

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Scan Tool Data Definitions

The HVAC Scan Tool Data Definitions contain a brief description of all the scan tool parameters. This list is in alphanumeric order.

A/C High Side Pressure: The scan tool displays 0 to 4000 kPa (0 to 580 psi). This parameter represents the A/C refrigerant pressure sensor voltage signal converted to pressure.

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

A/C Off For WOT: The scan tool displays Yes or No. Yes indicates that the PCM has disabled the A/C compressor because the TP sensor signal is at wide open throttle.

A/C Pressure Disable: The scan tool displays Yes or No. Yes indicates that the PCM has disabled the A/C compressor due to excessive refrigerant pressure.

A/C Relay Circuit Status: The scan tool displays OK, Fault or Invalid. Represents the status of the A/C relay circuit.

A/C Relay Commanded: The scan tool displays On or Off. Represents the PCM commanded state of the A/C compressor clutch relay. The A/C compressor clutch should be engaged when A/C Relay Commanded displays On.

A/C Request Signal: The scan tool displays Yes or No. The PCM uses the A/C request signal in order to determine if A/C compressor operation is being requested by the HVAC control module.

ECT Sensor: The scan tool displays -40 to +215°C (-40 to +420°F). The reading represents the temperature of the engine coolant.

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Circuit Description

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.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

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.

Action Taken When the DTC Sets

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.

Conditions for Clearing the DTC

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. Use a scan tool in order to clear the diagnostic trouble code.

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.

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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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. 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. Use a scan tool in order to clear the diagnostic trouble code.

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 voltage is between 9.0-18.0 volts.
2. 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.

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 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. 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 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. 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. «AIR DELIVERY DESCRIPTION AND OPERATION»(/buick/century/vi-1997-2005/remont/manual-hvac-system/#hvac-systems-manual__air-delivery-description-and-operation)
2. «AIR TEMPERATURE DESCRIPTION AND OPERATION»(/buick/century/vi-1997-2005/remont/manual-hvac-system/#hvac-systems-manual__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. 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/manual-hvac-system/#hvac-systems-manual__air-temperature-description-and-operation) .
5. The following conditions may cause window fogging: Wet carpet or mats High humidity Interior water leak Blocked A/C evaporator drain tube Maximum passenger capacity Blocked body pressure relief valves
6. 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/manual-hvac-system/#hvac-systems-manual)
2. «HVAC COMPRESSOR CLUTCH DOES NOT DISENGAGE»(/buick/century/vi-1997-2005/remont/manual-hvac-system/#hvac-systems-manual)
3. «BLOWER MOTOR ALWAYS ON»(/buick/century/vi-1997-2005/remont/manual-hvac-system/#hvac-systems-manual)
4. «BLOWER MOTOR INOPERATIVE»(/buick/century/vi-1997-2005/remont/manual-hvac-system/#hvac-systems-manual)
5. «BLOWER MOTOR MALFUNCTION»(/buick/century/vi-1997-2005/remont/manual-hvac-system/#hvac-systems-manual)
6. «TOO HOT IN VEHICLE»(/buick/century/vi-1997-2005/remont/manual-hvac-system/#hvac-systems-manual)
7. «TOO COLD IN VEHICLE»(/buick/century/vi-1997-2005/remont/manual-hvac-system/#hvac-systems-manual)
8. «AIR DELIVERY IMPROPER»(/buick/century/vi-1997-2005/remont/manual-hvac-system/#hvac-systems-manual)
9. «VACUUM CONTROL SYSTEM DIAGNOSTIC»(/buick/century/vi-1997-2005/remont/manual-hvac-system/#hvac-systems-manual)
10. LEAK TESTING in Heating, Ventilation and Air Conditioning
11. DEFROSTING INSUFFICIENT in Heating, Ventilation and Air Conditioning
12. NOISE DIAGNOSIS - BLOWER MOTOR in Heating, Ventilation and Air Conditioning
13. NOISE DIAGNOSIS - AIR CONDITIONING (A/C) SYSTEM in Heating, Ventilation and Air Conditioning
14. 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.

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

2. This step checks for continuous operation of the blower motor.

3. The test lamp should not illuminate while connected to any of the blower motor control circuits when the blower motor switch is in the OFF position. Illumination of the test lamp during this step indicates a malfunctioning blower motor switch or a short to voltage on a blower motor control circuit.

4. Test the blower motor control circuit that illuminated the test lamp in Step 3.

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

6. This step tests the output from the blower motor switch. Loss of blower motor switch output would indicate a malfunctioning switch or a circuit malfunction in the supply voltage to the switch.

7. There are 2 ignition 3 voltage circuits at the HVAC control module. Test the circuit that provides supply voltage to the blower motor switch.

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

5. This step tests the output of the blower motor switch in each speed position and through each blower motor control circuit.

6. Test the circuit that did not illuminate the test lamp in Step 5.

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

7. The specified values are from the A/C System Performance Test.

15. The voltage will vary between 0-12 volts during normal operation. The HVAC control module connector must be connected during this step.

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

14. The voltage will vary between 0-12 volts during normal operation. The HVAC control module connector must be connected during this step.

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Calibration Procedure

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.

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1. Remove the front floor console. Refer to CONSOLE REPLACEMENT - FRONT FLOOR (D06) in Instrument Panel, Gages, and Console.
2. Remove the retaining screws from the HVAC control assembly.
3. Pull the HVAC control assembly out from the I/P.
4. Disconnect the electrical connectors and the vacuum harness from the HVAC control assembly.
5. Remove the HVAC control assembly.

Installation Procedure

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1. Connect the electrical connectors and the vacuum harness to the HVAC control assembly.
2. Install the HVAC control assembly into the I/P. 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 retaining screws to secure the HVAC control assembly. 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.

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1. Remove the instrument panel accessory trim plate. Refer to TRIM PLATE REPLACEMENT - INSTRUMENT PANEL (I/P) ACCESSORY in Instrument Panel, Gages and Console.
2. Remove the screws from the HVAC control module.
3. Disconnect the electrical connectors from the HVAC control module.
4. Disconnect the vacuum connectors from the HVAC control vacuum valve.
5. Remove the HVAC control module from the instrument panel.
6. Remove the vacuum valve from the HVAC control module.

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1. Install the vacuum valve to the HVAC control module.
2. Connect the electrical connectors to the HVAC control module.
3. Connect the vacuum connectors to the HVAC control vacuum valve.
4. Install the HVAC control module to the instrument panel. NOTE: Refer to «FASTENER NOTICE»(/buick/century/vi-1997-2005/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
5. Install the screws to the HVAC control module. Tighten Tighten the screws to 2 N.m (18 lb ft).
6. Install the instrument panel accessory trim plate. Refer to TRIM PLATE REPLACEMENT - INSTRUMENT PANEL (I/P) ACCESSORY in Instrument Panel, Gages and Console.

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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.

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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 .

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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.

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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 .

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1. Remove the right instrument panel insulator panel. Refer to CLOSEOUT/INSULATOR PANEL REPLACEMENT - RIGHT in Instrument Panel, Gages and Console.
2. Remove the IP 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 the attachment to the HVAC module case.
6. Using the hand vacuum pump (2), open the recirculation actuator door to the full open 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.

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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.

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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.

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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.

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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 on 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.

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1. Install the recirculation actuator.
2. Connect the vacuum 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.

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

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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 or to CLOSEOUT/INSULATOR PANEL REPLACEMENT - LEFT in Instrument Panel, Gages and Console.

Air Delivery Description and Operation

The Air Delivery description and operation is divided into 3 areas

1. HVAC Control Components
2. Air Speed
3. Air Distribution

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 battery positive and ignition 3 voltage circuits provide power to the control assembly. Two integrated potentiometers control air temperature door position and blower motor speed. The integrated vacuum system controls the mode door position. The control assembly supports the following features

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Air Speed

The HVAC control module applies voltage to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request

1. Low speed-4 resistors
2. Medium 1 speed-3 resistors
3. Medium 2 speed-2 resistors
4. Medium 3 speed-1 resistor

When the operator requests High speed, the HVAC control module applies voltage to the blower motor relay through the high blower motor control circuit. The voltage energizes the blower motor relay, connecting the blower motor to battery positive voltage.

Vent Mode

When the operator selects VENT, the A/C Bi-level mode actuator has vacuum applied to it through the Blue vacuum line, making the vent door open. The heater/defroster actuator has vacuum applied to it through the Red vacuum line, making the defrost door close and the heater door open through mechanical linkage.

Bi-Level Mode

When the operator selects Bi-Level, the following occurs

1. The A/C Bi-level mode actuator is in neutral position.
2. The heater/defroster actuator has vacuum applied to it through the Red vacuum line.
3. The heater/defroster 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 A/C Bi-level mode actuator has vacuum applied to it through the Brown vacuum line, pushing the vent door closed. The heater/defroster 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 A/C Bi-level mode actuator has vacuum applied to it through the Brown vacuum line, pushing the vent door closed.
2. Vacuum is bled off the heater/defroster 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.

Defrost Mode

When the operator selects Defrost, the following occurs

1. The A/C Bi-level mode actuator has vacuum applied to it through the Brown vacuum line, pushing the vent door closed.
2. The heater/defroster 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.

Air Temperature Description and Operation

The air temperature controls are divided into 4 areas

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

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 battery positive and ignition 3 voltage circuits provide power to the HVAC control module. Three integrated potentiometers control air temperature door position and blower motor speed. The integrated vacuum system controls the mode door position. The HVAC control module supports the following features

Scheme 77

Air Temperature Actuator

The actuator is a 3 wire bi-directional electric motor. Ignition 3 voltage, ground and control circuits enable the actuator to operate. The control circuit uses a 0-12 volt linear-ramped signal to command the actuator movement. The 0 and 12 volt control values represent the opposite limits of the actuator range of motion. The values in between 0 and 12 volt correspond to the positions between the limits.

When the HVAC control module sets a commanded, or targeted, value, the control signal is set to a value between 0-12 volts. The actuator shaft rotates until the commanded position is reached. The module will maintain the control value until a new commanded value is needed.

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 2979 kPa (432 psi). The clutch will be enabled after the pressure decreases to less than 1510 kPa (219 psi).
2. A/C pressure is less than 186 kPa (27 psi). The clutch will be enabled after the pressure increased to more 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 A/C system can be engaged by pressing the A/C switch or by selecting the following modes

1. Max A/C
2. Mix-Blend
3. Front Defrost

The A/C LED will not illuminate unless the driver presses the A/C request switch on the HVAC control module. Otherwise, the A/C system may be running without the A/C LED indicator illuminated. The following conditions must be met in order for the PCM to turn on the compressor clutch

1. Ambient air temperature is above 4°C (40°F)
2. Engine coolant temperature (ECT) is less than 124°C (255°F) for the LG8 and 121°C (250°F) for the L36/L67
3. Engine speed is less than 5000 RPM
4. A/C Pressure is between 186-2979 kPa (27-432 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 2979 kPa (432 psi)
3. A/C Pressure is less than 186 kPa (27 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 switch allows the passenger to offset air discharge temperatures on the right side of the vehicle. To activate the dual zone, the passenger slides the switch to the desired offset. 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.

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 from, or condenses, and is discharged from the HVAC module as water.

Scheme 78

See also:
• FASTENER NOTICE
• AIR DELIVERY DESCRIPTION AND OPERATION
• AIR TEMPERATURE DESCRIPTION AND OPERATION
• HVAC COMPRESSOR CLUTCH DOES NOT ENGAGE