HVAC Systems - Automatic Buick LaCrosse I

Fastener Tightening Specifications

Fastener Tightening Specifications

Sensor Resistance Table

Sensor Resistance Table

Scheme 1

Scheme 2

Scheme 3

Scheme 4

Scheme 5

Scheme 6

Scheme 7

Scheme 8

HVAC Connector End Views

A/C Compressor Clutch Connector Part Information OEM: 12162017 Service: 12101937 2-Way F Metri-Pack 150 Series Sealed (GY) Pin Wire Color Circuit No. Function A D-GN 59 A/C Compressor Clutch Supply Voltage B BK 1050 Ground (L26) BK 1450 Ground (LY7)

A/C Refrigerant Pressure Sensor (L26) Connector Part Information OEM: 15344137 Service: 15306432 3-Way F GT 150 Series Flexlock Sealed (BK) Pin Wire Color Circuit No. Function 1 BK 2751 Low Reference 2 GY 2700 5-Volt Reference 3 RD/BK 380 A/C Refrigerant Pressure Sensor Signal

A/C Refrigerant Pressure Sensor (LY7) Connector Part Information OEM: Assembly 15477863 Connector 15478315 Connector Seal 15439078 Service: See Catalog 3-Way F GT 150 Series Sealed (BK) Pin Wire Color Circuit No. Function 1 BK 2759 Low Reference 2 GY 2709 5-Volt Reference 3 RD/BK 380 A/C Refrigerant Pressure Sensor Signal

Air Temperature Actuator - Left Connector Part Information OEM: 12059110 Service: 88953271 2-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function A YE 1791 Left Air Temperature Door Control A B D-BU/WH 1199 Left Air Temperature Door Control B

Air Temperature Actuator - Right Connector Part Information OEM: 12059110 Service: 88953271 2-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function A WH/BK 1236 Right Air Temperature Door Control A B D-BU 1646 Right Air Temperature Door Control B

Air Temperature Sensor - Inside Connector Part Information OEM: 10738109 (Delphi) 49901221 (Cinch) Service: See Catalog 6-Way F Quadlok Micro (BK) Pin Wire Color Circuit No. Function 1 PK 739 Ignition 1 Voltage 2 - - Not Used 3 BK/WH 1551 Ground 4 D-GN 734 Inside Air Temperature Sensor Signal 5 - - Not Used 6 GY 720 Low Reference

Air Temperature Sensor - Lower Left Connector Part Information OEM: 12047662 Service: 12085535 2-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function A TN/WH 518 Lower Left Air Temperature Sensor Signal B YE 61 Low Reference

Air Temperature Sensor - Lower Right Connector Part Information OEM: 12047662 Service: 12085535 2-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function A TN/BK 520 Lower Right Air Temperature Sensor Signal B OG/BK 1057 Low Reference

Air Temperature Sensor - Upper Left Connector Part Information OEM: 12047662 Service: 12085535 2-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function A BK 516 Upper Left Air Temperature Sensor Signal B BN 718 Low Reference

Air Temperature Sensor - Upper Right Connector Part Information OEM: 12047662 Service: 12085535 2-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function A TN 517 Upper Right Air Temperature Sensor Signal B PU 719 Low Reference

Blower Motor Connector Part Information OEM: 12084957 Service: 12126461 2-Way F Metri-Pack 280 Series (BK) Pin Wire Color Circuit No. Function A PU 65 Blower Motor Supply Voltage B BK 2150 Ground

Blower Motor Control Processor Connector Part Information OEM: 12041429 Service: 12167129 5-Way F Metri-Pack 280 Series (BK) Pin Wire Color Circuit No. Function A BK 1450 Ground B GY/BK 754 Blower Motor Speed Control C RD 442 Battery Positive Voltage D BK 2150 Ground E PU 65 Blower Motor Supply Voltage

HVAC Control Module C1 Connector Part Information OEM: 12110259 Service: 12110259 16-Way F Micro-Pack 100 Series (GN) Pin Wire Color Circuit No. Function A1 OG 1040 Battery Positive Voltage A2 PK 739 Ignition 1 Voltage A3 WH 1038 HVAC Class 2 Serial Data A4 - - Not Used A5 GY 8 Instrument Panel Lamp Supply Voltage A6 BK 1450 Ground A7 D-GN 734 Inside Air Temperature Sensor Signal A8 GY 720 Low Reference B1 BK 516 Upper Left Air Temperature Sensor Signal B2 - - Not Used B3 TN 517 Upper Right Air Temperature Sensor Signal B4 PU 719 Low Reference B5 L-BU/BK 590 Driver Sunload Sensor Signal B6 GY 1548 Passenger Sunload Sensor Signal B7 BN 718 Low Reference B8 BK/WH 1551 Ground

HVAC Control Module C2 Connector Part Information OEM: 12084944 Service: 12084944 16-Way F Micro-Pack 100 Series (BK) Pin Wire Color Circuit No. Function A1 TN/WH 518 Lower Left Air Temperature Sensor Signal A2 YE 61 Low Reference A3 TN/BK 520 Lower Right Air Temperature Sensor Signal A4 OG/BK 1057 Low Reference A5-A6 - - Not Used A7 GY/BK 754 Blower Motor Speed Control A8 - - Not Used B1 L-GN/BK 1647 Recirculation Door Control A B2 PK/WH 1648 Recirculation Door Control B B3 YE 1791 Left Air Temperature Door Control A B4 D-BU/WH 1199 Left Air Temperature Door Control B B5 WH/BK 1236 Right Air Temperature Door Control A B6 D-BU 1646 Right Air Temperature Door Control B B7 TN 2273 Mode Door Control A B8 L-GN 2275 Mode Door Position Signal

Mode Actuator Connector Part Information OEM: 12047781 Service: 12101864 3-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function A TN 2273 Mode Door Control A B - - Not Used C L-GN 2275 Mode Door Position Signal

Recirculation Actuator Connector Part Information OEM: 12059110 Service: 88953271 2-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function A L-GN/BK 1647 Recirculation Door Control A B PK/WH 1648 Recirculation Door Control B

Sunload Sensor Assembly Connector Part Information OEM: 12064760 Service: See Catalog 4-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function A L-BU/BK 590 Driver Sunload Sensor Signal B GY 1548 Passenger Sunload Sensor Signal C BK/WH 1551 Ground D L-GN/BK 1137 DRL Ambient Light Sensor Signal

DIAGNOSTIC CODE INDEX

DIAGNOSTIC CODE INDEX

Scan Tool Output Controls

HVAC Control Module Scan Tool Output Controls

PCM Scan Tool Output Controls

Scan Tool Data List

Use the Scan Tool Data Display Values and Definitions Information in order to assist in diagnosing the HVAC system. 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).

HVAC Scan Tool Data List

BCM Scan Tool Data List

PCM Scan Tool Data List

Scan Tool Data Definitions

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.

Circuit Description

Air temperature sensors allow the HVAC control module to monitor the discharge duct air, outside air and inside air temperatures. The HVAC control module provides ground to the air temperature sensor through the low reference circuit. The HVAC control module monitors the voltage drop across the air temperature sensor thermistor by supplying a 5 volt reference to the signal circuit of the air temperature sensor for automatic control calculations. When the air temperatures are cold, the resistances of the sensors are high and the voltage signals are high. When the air temperatures are hot, the resistances of the sensors are low and the voltage signals are low. The HVAC control module can read voltage values and count values where 1 volt is approximately equal to 51 counts.

1. Outside Air Temperature Sensor refers to the ambient air temperature sensor.
2. Passenger Compartment Temperature Sensor refers to the inside air temperature sensor.
3. Output Air Temperature Sensor 1 refers to the upper left air temperature sensor.
4. Output Air Temperature Sensor 2 refers to the lower left air temperature sensor.
5. Output Air Temperature Sensor 3 refers to the upper right air temperature sensor.
6. Output Air Temperature Sensor 4 refers to the lower right air temperature sensor.

DTC Descriptors

This diagnostic procedure supports the following DTCs

1. DTC B0159 Outside Air Temperature Sensor Circuit Range/Performance
2. DTC B0164 Passenger Compartment Temperature Sensor Circuit Range/Performance
3. DTC B0174 Output Air Temperature Sensor 1 Circuit Range/Performance
4. DTC B0179 Output Air Temperature Sensor 2 Circuit Range/Performance
5. DTC B0510 Output Air Temperature Sensor 3 Circuit Range/Performance
6. DTC B0515 Output Air Temperature Sensor 4 Circuit Range/Performance

Conditions for Running the DTC

1. Battery voltage is within 8.7-16.5 volts.
2. The ignition is ON.

Conditions for Setting the DTC

The HVAC control module determines that the value of the air temperature parameter is less than 5 counts or greater than 250 counts.

Action Taken When the DTC Sets

The air temperature sensors operate using a default value. The default values are not displayed on the scan tool.

Conditions for Clearing the DTC

1. The DTC will become history if the HVAC control module no longer detects a fault.
2. The history DTC will clear after 100 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

Test Description

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

1. 2: Verifies that the temperature displayed is not within the calibrated range.
2. 3: Tests for the proper operation of the circuit in the high voltage range.
3. 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.

DTC B0159, B0164, B0174, B0179, B0510 or B0515

The sunload sensor is a 2-wire photo diode. The vehicle uses left and right sunload sensors. The two sensors are integrated into the sunload sensor assembly along with the ambient light sensor. Low reference and signal circuits enable the sensor to operate. As the sunload increases, the sensor signal decreases. 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.

1. Sunload sensor 1 refers to the left sunload sensor
2. Sunload sensor 2 refers to the right sunload sensor

This diagnostic procedure supports the following DTCs

1. DTC B0184 Sunload Sensor 1 Circuit Performance
2. DTC B0189 Sunload Sensor 2 Circuit Performance

The ignition is turned ON.

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

1. If the DTC sets due to a low voltage condition, the HVAC control module will operate the system as if a minimum sunload condition exists.
2. If the DTC sets due to a high voltage condition, the HVAC control module will operate the system as if a minimum sunload condition exists.

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.

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

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

DTC B0184 or B0189

The actuator is an electronic stepper motor. The HVAC control module supplies power and ground to the actuator. The HVAC control module controls the direction of the actuator by changing the polarity of the control circuits. When the actuator reaches its desired position, both circuits are fixed to the same value 0 volts. The HVAC control module determines the door or mode film position by counting pulses (voltage fluctuations) caused by the brush to commutator action generated during normal motor operation. The HVAC control module monitors a voltage drop across an internal resistance to detect the pulses. The HVAC control module converts the pulses to counts with a range of 0-255 counts.

When a calibration or recalibration procedure is performed, the HVAC control module calculates the door or mode film travel range. The HVAC control module commands the actuator in one extreme position then counts pulses starting from 0 counts. The HVAC control module compares the total number of pulses to calibrated limits. If the total pulse count is less than or equal to the maximum calibrated limit and greater than or equal to the minimum calibrated limit, then the calibration is considered successful.

1. Air flow control 3 circuit refers to the mode actuator.
2. Air flow control 7 circuit refers to the recirculation actuator.
3. Temperature control 1 circuit refers to the left air temperature actuator.
4. Temperature control 2 circuit refers to the right air temperature actuator.

This diagnostic procedure supports the following DTCs

1. DTC B0249 Air Flow Control 3 Circuit Range
2. DTC B0269 Air Flow Control 7 Circuit Range
3. DTC B0409 Temperature Control 1 Circuit Range
4. DTC B0419 Temperature Control 2 Circuit Range

The HVAC control module will run the DTC when either of the following conditions are met.

1. The HVAC control module has completed a calibration/recalibration of the actuator.
2. The HVAC control module commands the actuator to move.

The HVAC control module will set this DTC if either of the following conditions are true.

1. The actuator fails calibration/recalibration due to an over travel or under travel condition. The HVAC control module does not detect the calibrated number of total pulse counts during a travel range check.
2. The HVAC control module determines that the actual door position does not equal the commanded door position. The HVAC control module commands the door to move but does not see the expected number of pulses between positions.

1. The HVAC control module will attempt to make use of whatever range is still available.
2. The HVAC control module will recalibrate the actuator each time the ignition switch is turned ON.

Conditions for Clearing the MIL/DTC

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 100 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

Diagnostic Aids

1. Inspect the appropriate actuator door and actuator for the following conditions: A misaligned actuator-Refer to «Mode Actuator Replacement»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic) , «Air Temperature Actuator Replacement - Right»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic) , «Air Temperature Actuator Replacement - Left»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic) or «Recirculation Actuator Replacement»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic) . Broken or binding mode actuator film or actuator door Obstruction that prevents the mode film or actuator door from operating within its full range of motion Missing seals to the actuator door Misaligned seals to the actuator door
2. Refer to «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/i-2004-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing) in Wiring Systems.

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

1. 2: This step verifies that the HVAC control module is able to command the actuator through its full range of motion.
2. 4: If the actuator does not move at all, the problem is likely to be the drive circuitry within the HVAC control module, the actuator or the wiring harness. If the actuator does move, but not within its full range of motion, the problem is likely to be a mechanical binding of the actuator door or actuator door linkage.
3. 6: This step drives the actuator in one direction. The actuator shaft will not move if the actuator door is already in the position you are attempting to drive it to.
4. 7: This step drives the actuator in the opposite direction.

DTC B0249, B0269, B0409 or B0419

The actuator is an electronic stepper motor. The HVAC control module supplies power and ground to the actuator. The HVAC control module controls the direction of the actuator by changing the polarity of the control circuits. When the actuator reaches its desired position, both circuits are fixed to the same value 0 volts. The HVAC control module determines the door or mode film position by counting pulses, voltage fluctuations, caused by the brush to commutator action generated during normal motor operation. The HVAC control module monitors a voltage drop across an internal resistance to detect the pulses. The HVAC control module converts the pulses to counts with a range of 0-255 counts.

When a calibration or recalibration procedure is performed, the HVAC control module calculates the door or mode film travel range. The HVAC control module commands the actuator in one extreme position then counts pulses starting from 0 counts. The HVAC control module compares the total number of pulses to calibrated limits. If the total pulse count is less than or equal to the maximum calibrated limit and greater than or equal to the minimum calibrated limit, then the calibration is considered successful.

1. Air flow control 3 circuit refers to the mode actuator.
2. Air flow control 7 circuit refers to the recirculation actuator.
3. Temperature control 1 circuit refers to the left air temperature.
4. Temperature control 2 circuit refers to the right air temperature.

This diagnostic procedure supports the following DTCs

1. DTC B0414 Air Flow Control 3 Circuit
2. DTC B0424 Air Flow Control 7 Circuit
3. DTC B3748 Temperature Control 1 Circuit
4. DTC B3749 Temperature Control 2 Circuit

The ignition is turned ON. The inoperative actuator DTC runs during and after the next range check following the setting of the actuator range error DTC. The appropriate actuator inoperative code will set with the appropriate actuator range error code.

1. DTC B0414 Air Flow Control 3 Circuit Range
2. DTC B0424 Air Flow Control 7 Circuit Range
3. DTC B3748 Temperature Control 1 Circuit Range
4. DTC B3749 Temperature Control 2 Circuit Range

The HVAC control module does not detect any movement of the actuator.

1. The HVAC control module will recalibrate the appropriate actuator each time the ignition switch is turned ON.
2. If DTC B0424 is set, the HVAC control module will command the recirculation door to the outside air position.

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 100 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

1. Inspect the actuator door and actuator for the following conditions: A misaligned actuator-Refer to «Mode Actuator Replacement»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic) , «Air Temperature Actuator Replacement - Right»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic) , «Air Temperature Actuator Replacement - Left»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic) or «Recirculation Actuator Replacement»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic) . Broken or binding mode actuator film or actuator door Obstruction that prevents the mode film or actuator door from operating within its full range of motion Missing seals to the actuator door Misaligned seals to the actuator door
2. Refer to «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/i-2004-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing) in Wiring Systems.

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

1. 2: This step verifies that the HVAC control module is able to command the appropriate actuator through its full range of motion.
2. 4: If the actuator does not move at all, the problem is likely to be the drive circuitry within the HVAC control module, the actuator or the wiring harness. If the actuator does move, but not within its full range of motion, the problem is likely to be a mechanical binding of the actuator door or actuator door linkage.
3. 6: This step drives the actuator in one position. The actuator shaft will not move if the actuator door is already in the position you are attempting to drive it to.
4. 7: This step drives the actuator in the opposite direction.

DTC B0414, B0424, B3748 or B3749

The engine control module (ECM)/powertrain control module (PCM) monitors the high side refrigerant pressure via the A/C refrigerant pressure sensor. The ECM/PCM applies a 5-volt reference and a low reference to the sensor. Changes in the A/C refrigerant pressure cause the A/C refrigerant pressure sensor signal to the ECM/PCM to vary. 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 ECM/PCM commands the cooling fans on. When pressure is too high or too low the ECM/PCM will not allow the A/C compressor clutch to engage. When the DTC is set, the ECM/PCM does not allow the A/C compressor clutch to engage. This is done to protect the compressor.

This diagnostic procedure supports the following DTCs

1. DTC P0530 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit
2. DTC P0532 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit Low Voltage
3. DTC P0533 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit High Voltage

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

P0530

The A/C refrigerant pressure sensor signal voltage is less than 0.2 volt or more than 4.88 volts for more than 3 seconds.

P0532

The A/C refrigerant pressure sensor signal voltage is less than 0.2 volt for more than 3 seconds.

P0533

The A/C refrigerant pressure sensor signal voltage is more than 4.88 volts for more than 3 seconds.

1. The ECM/PCM stores the DTC information into memory when the diagnostic runs and fails.
2. The malfunction indicator lamp (MIL) will not illuminate.
3. The ECM/PCM disables the A/C compressor clutch.
4. The ECM/PCM records the operating conditions at the time the diagnostic fails. The ECM/PCM stores this information in the Failure Records.
5. The ECM/PCM will report a value of 0 kPa to the HVAC control module.
6. The driver information center will display SERVICE A/C SYSTEM.
7. The A/C OFF segment will illuminate on the HVAC control module.

1. A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
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 DTC P0532 or P0533 cannot be duplicated, reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.

If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

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

1. 3: This step tests for the proper operation of the circuit in the low voltage range.
2. 4: This step tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to ground.
3. 5: This step tests for a short to voltage in the 5-volt reference circuit.

DTC P0530, P0532 or P0533

Ignition voltage is supplied directly to the A/C compressor clutch relay. The engine control module (ECM)/powertrain control module (PCM) controls the relay by grounding the A/C clutch relay control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. The driver has a fault line which is monitored by the ECM/PCM. When the ECM/PCM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the ECM/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 ECM/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

When the ECM/PCM detects any of the above malfunctions, this DTC is set and the affected driver is disabled.

This diagnostic procedure supports the following DTCs

1. DTC P0645 Air Conditioning (A/C) Clutch Relay Control Circuit
2. DTC P0646 Air Conditioning (A/C) Clutch Relay Control Circuit Low Voltage
3. DTC P0647 Air Conditioning (A/C) Clutch Relay Control Circuit High Voltage

1. The ignition voltage is between 9-18 volts.
2. The engine speed is more than 80 RPM.
3. The ECM/PCM driver transitions from ON to OFF or from OFF to ON.

P0645

The ECM/PCM detects an open on the control circuit of the A/C compressor clutch relay.

P0646

The ECM/PCM detects a short to ground on the control circuit of the A/C compressor clutch relay.

P0647

The ECM/PCM detects a short to voltage on the control circuit of the A/C compressor clutch relay.

1. The ECM/PCM will not illuminate the malfunction indicator lamp (MIL).
2. The ECM/PCM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

1. A History DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction.
2. The DTC can be cleared by using a scan tool.

If DTC P0645, P0646, P0647 cannot be duplicated, reviewing the Failure Records vehicle millage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.

If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

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

1. 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.
2. 3: This step tests for voltage at the coil side of the A/C compressor clutch relay. The 10-amp fuse supplies power to the coil side of the A/C compressor clutch relay.
3. 4: This step verifies that the engine control module is providing ground to the A/C compressor clutch relay. If light always on circuit shorted to ground.
4. 8: This step tests for a short to voltage or an open.
5. 10: If the A/C fuse is open ensure to test the A/C compressor clutch supply voltage circuit for short to ground.

DTC P0645, P0646 or P0647

1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/i-2004-2009/remont/oem-general-information/#vehicle-dtc-information) in Vehicle DTC Information, before using the Symptom Tables in order to verify that all of the following are true: There are no DTCs set. The control modules can communicate via the serial data link.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to the following information: «Air Delivery Description and Operation»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic__air-delivery-description-and-operation) «Air Temperature Description and Operation»(/buick/lacrosse/i-2004-2009/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»(/buick/lacrosse/i-2004-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing__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 auxiliary HVAC controls.
5. The A/C compressor will not operate in cold outside air temperatures. Refer to «Air Temperature Description and Operation»(/buick/lacrosse/i-2004-2009/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 leak 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 Conditions 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/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic)
2. «HVAC Compressor Clutch Does Not Disengage»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic__hvac-compressor-clutch-does-not-disengage)
3. «Blower Motor Always On»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic__blower-motor-always-on)
4. «Blower Motor Inoperative»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic__blower-motor-inoperative)
5. «Blower Motor Malfunction»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic)
6. «Too Hot in Vehicle»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic)
7. «Too Cold in Vehicle»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic)
8. «Air Delivery Improper»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic)
9. «Air Recirculation Malfunction»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic)
10. «Leak Testing»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) in Heating, Ventilation and Air Conditioning
11. «Noise Diagnosis - Blower Motor»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-blower-motor) in Heating, Ventilation and Air Conditioning
12. «Noise Diagnosis - Air Conditioning (A/C) System»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-air-conditioning-ac) in Heating, Ventilation and Air Conditioning
13. «Odor Diagnosis»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__odor-diagnosis) in Heating, Ventilation and Air Conditioning

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

1. 2: The air conditioning (A/C) compressor relay output is disabled if engine coolant temperature is above 124°C (255°F).

1. 3: Placing the fan switch in the ON position, 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.
2. 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.

HVAC Compressor Clutch Does Not Engage

HVAC Compressor Clutch Does Not Disengage

HVAC Compressor Clutch Does Not Disengage

Blower Motor Always On

Blower Motor Always On

Blower Motor Inoperative

Blower Motor Inoperative

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

1. 2: This step will determine if one or more blower speeds are inoperative.
2. 3: This step determines if the HVAC control module and blower motor control processor are attempting to control the blower motor speed.
3. 5: The measured voltage on the blower motor speed control circuit should steadily decrease from 4.6-1.1 volts as the blower motor speed is adjusted from the minimum speed position to the maximum speed position.

Blower Motor Malfunction

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

1. 5: The ambient air temperature must be above 3°C (38°F) for this A/C compressor test.
2. 6: The specified values are from the A/C System Performance Test.

Too Hot in Vehicle

1. 2: This test resets HVAC control module and checks for current air temperature actuator DTC.
2. 8: This checks for proper operation of coolant system to insure heater output.

Too Cold in Vehicle

1. The condition may be intermittent. Refer to «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/i-2004-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing) in Wiring Systems.
2. Inspect the air delivery system for the following conditions: A dirty HVAC air filter An obstruction to the airflow Air leaks Misaligned air ducts Broken or binding linkages or doors

Air Delivery Improper

1. If the control A circuit of the recirculation actuator is shorted to ground, the following conditions will occur. The recirculation actuator will operate properly when recirculation is requested. The recirculation actuator will continually modulate between the outside air and recirculation positions when outside air is requested.
2. If the control B circuit of the recirculation actuator is shorted to ground, the following conditions will occur. The recirculation actuator will operate properly when outside air is requested. The recirculation actuator will continually modulate between the outside air and recirculation positions when recirculation is requested.
3. The condition may be intermittent. Refer to «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/i-2004-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing) in Wiring Systems.
4. Inspect the recirculation door and the recirculation actuator for the following conditions: A misaligned recirculation actuator-Refer to «Recirculation Actuator Replacement»(/buick/lacrosse/i-2004-2009/remont/automatic-hvac-system/#hvac-systems-automatic) . Broken or binding linkages A broken or binding recirculation door An obstruction that prevents the recirculation door from operating within its full range of motion Missing seals to the recirculation door Misaligned seals to the recirculation door

Air Recirculation Malfunction

Re-Calibrating Actuators

When replacing the HVAC control module it will be necessary to allow the HVAC control module to perform a calibration process. When installing the HVAC control module be sure to perform the following

1. Place the ignition switch to the OFF position.
2. Disconnect the scan tool.
3. Install the HVAC control module.
4. Connect all previously disconnected components.
5. Start the vehicle.
6. Wait 40 seconds for the HVAC control module to self-calibrate.
7. Verify that no DTCs have set as current DTCs.

When replacing the HVAC actuator it will be necessary to allow the HVAC control module to perform a calibration process. When installing the HVAC actuator be sure to perform one of the following

Preferred Method (w/Scan Tool)

1. Clear all DTCs.
2. Place the ignition switch in the OFF position.
3. Install the HVAC actuator.
4. Connect all previously disconnected components.
5. Start the vehicle.
6. With the scan tool, initiate the Motor Re-calibration feature of the Heating and Air Conditioning Special Functions menu.
7. Verify that no DTCs have set as current DTCs.

Alternate Method (w/o Scan Tool)

1. Clear all DTCs.
2. Place the ignition switch to the OFF position.
3. Install the HVAC actuator.
4. Connect all previously disconnected components.
5. Remove the HVAC/ECAS fuse for a minimum of 10 seconds.
6. Install the HVAC/ECAS fuse.
7. Start the vehicle.
8. Wait 40 seconds for the HVAC control module to self-calibrate.
9. Verify that no DTCs have set as current DTCs.

Removal Procedure

1. Remove the instrument panel lower trim plate. Refer to «Trim Plate Replacement - Instrument Panel (I/P) Lower (w/Floor Console)»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
2. Remove the HVAC control module mounting screws (1).
3. Pull the HVAC control module rearward from the instrument panel.
4. Disconnect the electrical connectors form the HVAC control module.
5. Remove the HVAC control module.

Installation Procedure

1. Connect the electrical connectors to the HVAC control module.
2. Install the HVAC control module.
3. Install the HVAC control module mounting screws. Tighten: Tighten the screws to 2 N.m (18 lb in).
4. Install the instrument panel lower trim plate. Refer to «Trim Plate Replacement - Instrument Panel (I/P) Lower (w/Floor Console)»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
5. Start the engine and run for 1 minute.

1. Remove the right instrument panel (I/P) insulator. Refer to «Closeout/Insulator Panel Replacement - Right»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
2. Remove the I/P compartment. Refer to «Compartment Replacement - Instrument Panel (I/P)»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
3. Remove the screws that secure the recirculation actuator to the HVAC module assembly.
4. Remove the recirculation actuator from the HVAC module assembly.
5. Disconnect the electrical connector from the recirculation actuator.

1. Position the recirculation actuator, aligning the slots in the electric actuator drive to the flats on the shaft.
2. Align the locating hole to the alignment pin on the HVAC module assembly.
3. Slide the actuator drive completely onto the shaft, with the mounting holes flush with the mounting screw holes on the HVAC module assembly.
4. Install the screws to the recirculation actuator. Tighten: Tighten the screws to 1.5 N.m (13 lb in).
5. Connect the electrical connector to the recirculation actuator.
6. Install the I/P compartment. Refer to «Compartment Replacement - Instrument Panel (I/P)»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
7. Install the right I/P insulator. Refer to «Closeout/Insulator Panel Replacement - Right»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
8. Calibrate the actuator. Refer to «Re-Calibrating Actuators»(/buick/lacrosse/i-2004-2009/remont/manual-hvac-system/#hvac-systems-manual) .

1. Remove the right instrument panel (I/P) insulator. Refer to «Closeout/Insulator Panel Replacement - Right»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
2. Remove the I/P compartment. Refer to «Compartment Replacement - Instrument Panel (I/P)»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
3. Remove the screws that secure the mode actuator (1) to the HVAC module assembly.
4. Remove the mode actuator from the HVAC module assembly.
5. Disconnect the electrical connector from the mode actuator.

1. Position the mode actuator, aligning the slots in the electric actuator drive to the flats on the shaft.
2. Align the locating hole to the alignment pin on the HVAC module assembly.
3. Slide the actuator drive completely onto the shaft, with the mounting holes flush with the mounting screw holes on the HVAC module assembly.
4. Install the screws to the mode actuator (1). Tighten: Tighten the screws to 1.5 N.m (13 lb in).
5. Connect the electrical connector to the mode actuator.
6. Install the I/P compartment. Refer to «Compartment Replacement - Instrument Panel (I/P)»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
7. Install the right I/P insulator. Refer to «Closeout/Insulator Panel Replacement - Right»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
8. Calibrate the actuator. Refer to «Re-Calibrating Actuators»(/buick/lacrosse/i-2004-2009/remont/manual-hvac-system/#hvac-systems-manual) .

1. Remove the right side instrument panel (I/P) insulator. Refer to «Closeout/Insulator Panel Replacement - Right»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
2. Remove the I/P compartment. Refer to «Compartment Replacement - Instrument Panel (I/P)»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
3. Remove the screws retaining the air temperature actuator (2).
4. Disconnect the electrical connector from the air temperature actuator.
5. Remove the air temperature actuator from the HVAC Module Assembly.

1. Position the air temperature actuator (2). 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 the shaft. The actuator driver should sit completely on the shaft and the mounting holes should be flush with the HVAC module case.
4. Install the screws to the air temperature actuator. Tighten: Tighten the screw to 1.5 N.m (13 lb in).
5. Connect the electrical connector to the air temperature actuator.
6. Install the I/P compartment. Refer to «Compartment Replacement - Instrument Panel (I/P)»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
7. Install the right side I/P insulator. Refer to «Closeout/Insulator Panel Replacement - Right»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
8. Calibrate the actuator. Refer to «Re-Calibrating Actuators»(/buick/lacrosse/i-2004-2009/remont/manual-hvac-system/#hvac-systems-manual) .

1. Remove the left closeout panel. Refer to «Closeout/Insulator Panel Replacement - Left»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
2. Disconnect the electrical connector from the left air temperature actuator.
3. Remove the mounting screws from the left air temperature actuator.
4. Remove the left air temperature actuator.

1. Position the left air temperature actuator. 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 on the shaft. The actuator driver should seat completely onto the shaft and the mounting holes should be flush with the mounting screws on the HVAC module case.
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 left closeout panel. Refer to «Closeout/Insulator Panel Replacement - Left»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
7. Calibrate the actuator. Refer to «Re-Calibrating Actuators»(/buick/lacrosse/i-2004-2009/remont/manual-hvac-system/#hvac-systems-manual) in HVAC Systems - Manual.

1. Remove the radio. Refer to «Radio Replacement»(/buick/lacrosse/i-2004-2009/remont/entertainment-systems/#entertainment-systems) in Entertainment.
2. Remove the upper right air temperature sensor from the center air duct.
3. Disconnect the electrical connector from the upper right air temperature sensor.

1. Install the upper right air temperature sensor to the center air duct.
2. Connect the upper right air temperature sensor electrical connector.
3. Install the radio. Refer to «Radio Replacement»(/buick/lacrosse/i-2004-2009/remont/entertainment-systems/#entertainment-systems) in Entertainment.

1. Remove the radio. Refer to «Radio Replacement»(/buick/lacrosse/i-2004-2009/remont/entertainment-systems/#entertainment-systems) in Entertainment.
2. Remove the upper left air temperature sensor from the center air duct.
3. Disconnect the electrical connector from the upper left air temperature sensor.

1. Install the upper left air temperature sensor to the center air duct.
2. Connect the upper left air temperature sensor electrical connector.
3. Install the radio. Refer to «Radio Replacement»(/buick/lacrosse/i-2004-2009/remont/entertainment-systems/#entertainment-systems) in Entertainment.

1. Remove the left closeout panel. Refer to «Closeout/Insulator Panel Replacement - Left»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
2. Remove the lower left air temperature sensor from the heater outlet cover.
3. Disconnect the electrical connector from the lower left air temperature sensor.

1. Install the lower left air temperature sensor to the heater outlet cover.
2. Connect the lower left air temperature sensor electrical connector.
3. Install the left closeout panel. Refer to «Closeout/Insulator Panel Replacement - Left»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.

1. Remove the right closeout panel. Refer to «Closeout/Insulator Panel Replacement - Right»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
2. Remove the lower right air temperature sensor from the heater outlet cover.
3. Disconnect the electrical connector from the lower right air temperature sensor.

1. Install the lower right air temperature sensor to the heater outlet cover.
2. Connect the lower right air temperature sensor electrical connector.
3. Install the right closeout panel. Refer to «Closeout/Insulator Panel Replacement - Right»(/buick/lacrosse/i-2004-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.

1. Remove the upper air deflector. Refer to «Radiator Air Baffle and Deflector Replacement - Upper»(/buick/lacrosse/i-2004-2009/remont/cooling-system-mechanical/#engine-cooling-system) in Engine Cooling.
2. Push inward on the retaining tabs (1) to disengage the ambient air temperature sensor.
3. Disconnect the electrical connector from the ambient air temperature sensor.

1. Connect the ambient air temperature sensor electrical connector to the ambient air temperature sensor.
2. Align the retaining tabs (1) to the bottom side of the ambient air temperature sensor hole.
3. Push upwards to install the ambient air temperature sensor to the vehicle.
4. Install the upper air deflector. Refer to «Radiator Air Baffle and Deflector Replacement - Upper»(/buick/lacrosse/i-2004-2009/remont/cooling-system-mechanical/#engine-cooling-system) in Engine Cooling.

Scheme 9

Inside Air Temperature Sensor Replacement

Scheme 10

Sun Load Sensor Replacement

Air Delivery Description and Operation

The air delivery controls are divided into 2 primary areas. The first, air speed, is dependent upon blower motor speed. The second, air distribution, is related to various single or multiple air outlets.

Air Speed

The blower motor forces air throughout the vehicles interior. The vehicle operator determines the blower motor's speed by toggling the blower motor switch manually or by using the automatic mode. The blower motor will always operate at some speed as long as the HVAC control module is in any position other than OFF, as long as the ignition switch is in the RUN position. The blower motor and mode switches are located within the HVAC control module.

Power is provided to the blower motor from the blower motor control processor through the blower motor supply voltage circuit. The blower motor control processor receives power from the under hood electrical center through the battery positive voltage circuit. Ground is provided by the blower motor control processor and ground circuit.

When any blower speed is selected, whether manual or automatic, the blower motor control processor will control blower motor speeds based on a 5-volt signal circuit that is pulse width modulated (PWM) signal by the HVAC control module. When a low blower speed is requested, the PWM signal is reduced. When a higher blower speed is requested, the PWM signal is increased. The blower motor control processor interprets the PWM signal and varies the ground on the blower motor control circuit internally. An open circuit, short to ground or short to battery on the blower motor speed control circuit will disrupt the PWM signal and cause the blower motor to not operate. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature. Toggling the blower button manually also activates the liquid crystal display (LCD) display for the blower speed selected.

Off Mode

When the vehicle is moving, air flowing over the vehicle increases the air pressure just ahead of the windshield. This forces air into the outside air inlet, into the HVAC module and out through the floor outlets. The HVAC control module attempts to match the inside air temperature and driver selected temperatures. Since the air conditioning (A/C) compressor is not running, the incoming air may be warmed but not cooled. Press the driver side air temperature switch to turn off the HVAC system. The ambient air temperature will show on the display.

Recirculation Mode

When the recirculation switch is pressed, the HVAC control module will apply a ground to one of the recirculation door control circuits in order to obtain the desired position. The recirculation actuator is a reverse polarity motor, each circuit provides both power and ground to the recirculation actuator. When the actuator is being held in a stationary position, both of the recirculation door control circuits have 12 volts applied to both sides of the actuator motor. This holds the actuator stationary. When a recirculate position is requested, one of the recirculation door control circuits will ground driving the recirculation actuator into the desired position. When an outside air position is requested, the other recirculation door control circuit will ground. This moves the recirculation actuator into an outside air position. This brings air from outside the vehicle instead of air from the inside.

The HVAC control module provides power and ground to the recirculation actuator. The HVAC control module receives power from the under hood electrical center through the ignition 3 voltage circuit. Ground is provided by the ground circuit.

The recirculation mode can be used in both automatic and manual operation. The only time recirculation is not available is when FRONT DEFROST and mix blend mode is selected. The RECIRC LED will flash to alert the driver that recirculation mode is not available. Pressing the recirculation switch, from the OFF position, will set the blower, mode and A/C compressor clutch into automatic mode.

When in automatic mode, recirculation will stay on until either the vehicle operator selects outside air, by pressing the RECIRCULATION switch or the HVAC control module automatically moves the recirculation actuator. Automatic recirculation is only available when air temperatures are 21°C (70°F) or warmer. The recirculation actuator position will vary to obtain a cooler duct air temperature when cool air is selected. This will assist in cooling the vehicle quicker.

The HVAC control module will move the recirculation actuator to the outside air position at ignition off to bring fresh air to replace stale air that has accumulated in the HVAC module during shut down.

When requested the recirculation actuator will be able to move to the 100 percent recirculation position for a limited time, after that limited time the actuator will move to the 90 percent position. In the auto mode only, the recirculation actuator will move faster to the recirculation position when vehicle is at an idle compared to the normal speed of the actuator during normal operation.

If the recirculation actuator or related circuits has a failure the HVAC control module will attempt to drive the actuator to the outside air position regardless of mode selection. If there is a failure with one of the air temperature actuators the HVAC control module will allow the recirculation actuator to move to the outside air position.

Automatic Modes

The automatic HVAC system will warm up/cool down and maintain the interior temperature of the vehicle by controlling the A/C compressor clutch, blower motor, air temperature, mode and recirculation actuators to achieve the desired temperature. For fully automatic operation, both the blower and mode buttons must be in the AUTO position. Blower speeds will change automatically based on inputs to the HVAC control module. The HVAC control module will always come back to the last settings after an ignition cycle or, if equipped, to the last settings of the driver by pressing the UNLOCK button on the remote keyless entry fob and placing the ignition in RUN. Only RECIRCULATION will have to be reset after each ignition cycle.

Moisture tends to accumulate in the HVAC module assembly after the engine has been shut OFF. The HVAC control module will purge the HVAC module of stale air and moisture to prevent window fogging. The mode actuator will move to the floor mode and run the low speed blower for 10 seconds to purge out the air and moisture. The recirculation actuator will be in the outside air position. Purge mode can be bypassed if any manual modes are selected.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. On cold engine start-up, when temperatures are -1°C (30°F) or colder, low blower speeds will be selected and airflow will be directed on the windshield for 3 minutes. This is done to prevent windshield fogging. To warm the interior quickly, maximum heat mode is used where the blower is at maximum speed, floor mode, both air temperature actuators are in full hot position and outside air is being drawn in. The vehicle operator can select the extreme warm setting of 32°C (90°F), but the system will be out of automatic operation and not warm the vehicle any faster or regulate the blower speed. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the HVAC control module.

In warm temperatures, the automatic HVAC system will provide A/C in the most efficient manner. On vehicle start-up, the HVAC control module will monitor for conditions that indicate the possible presence of moisture in the HVAC module. To avoid blowing hot air and moisture out at the driver, the HVAC control module moves the mode door toward the floor and runs the low speed blower for a 3 seconds. This purge mode can be bypassed if the vehicle is started with the blower switch in maximum speed position. To cool the interior quickly, maximum cool mode is used where the blower is at maximum speed, both air temperature actuators are in full cold position and the recirculation actuator is drawing air from inside the vehicle. The vehicle operator can select the extreme cool setting of 16°C (60°F), but the system will be out of automatic operation and not cool the vehicle any faster or regulate the blower speed. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the HVAC control module.

Air Distribution

When the mode switch is pressed, a ground is provided from the HVAC control module to the mode actuator through the mode door control circuits. When the mode actuator receives the signal, the mode actuator moves into the desired position.

The HVAC control module provides power and ground to the mode actuator. The HVAC control module receives power from the rear fuse block through the ignition 3 voltage circuit. Ground is provided by the ground circuit.

The mode actuator is a reverse polarity motor. Each circuit provides both power and ground to the mode actuator. When the mode actuator is being held in position, both of the mode door control circuits have 12 volts applied to both sides of the actuator motor. This holds the actuator stationary. When a mode is requested, one of the mode door control circuits will ground, driving the mode actuator into the desired mode.

Front Defrost Mode

The front defrost mode is the only setting that is not controlled by the automatic HVAC system. When defrost is selected, by the vehicle operator, the A/C compressor is activated and outside air is brought into the vehicle. The blower motor will be activated, regardless of coolant temperature and air will be directed toward the windshield, the side windows and some air flow to the floor. Recirculation mode is not available in front defrost. The recirculation LED will flash on their respective displays if any of those switches are pressed when in front defrost mode. This indicates that these modes are not available. The rear window defogger does not affect the HVAC system in any setting.

Mode Switch

Use the MODE switch in order to change the air delivery mode in the vehicle. Selection of the MODE switch when in AUTO mode will lock in the air flow mode that AUTO was controlling. The system will stay in that mode until the MODE or AUTO switch is pressed. Toggling the MODE button also activates the LCD display for the mode selected. If an airflow mode is currently displayed, pressing the MODE button selects the next air flow mode. The air flow direction will sequence through the following modes

1. MIX-BLEND-Air is directed through the floor, windshield and side window outlets.
2. BI-LEVEL-Cool air is delivered through the vent outlets while warm air is delivered through the floor outlets.
3. FLOOR-Air is delivered though the floor, windshield and side window outlets.
4. VENT-Air is delivered through the instrument panel outlets.

These are the only air flow modes available through the MODE button. When in AUTO mode, the HVAC control module will only operate in the following modes

1. BI-LEVEL
2. VENT
3. FLOOR

Dual Zone Control Switch

The passenger air temperature switch is provided to allow the passenger to set air discharge temperatures on the passenger side of the vehicle. Passenger temperatures can be set from 15-32°C (60-90°F). To activate the dual zone, the passenger air temperature switch to the desired offset. If the passenger air temperature switch has been turned on, it can be turned off by pressing the passenger switch. Greater sunload on one side of the vehicle may cause the discharge air temperatures to be different, even when the HVAC system is not operating in a dual zone mode.

The HVAC control module provides power and ground to the passenger air temperature actuator. The HVAC control module receives power from the under hood electrical center through the ignition 3 voltage circuit. Ground is provided by the ground circuit.

The passenger air temperature actuator is a reverse polarity motor. Each circuit provides both power and ground to the passenger air temperature actuator. When the passenger air temperature actuator is being held in position, both of the passenger air temperature door control circuits have 12 volts applied to both sides of the actuator motor. This holds the actuator stationary. When a temperature offset is requested, one of the passenger air temperature door control circuits will ground, driving the passenger air temperature actuator into the desired temperature offset.

Remote Start Activation

The following describes the HVAC control head functionality upon receiving the remote start active serial data message and a power mode status is set to off a wake. Outside ambient temperature sensor, OAT- on automatic systems or intake air temperature (IAT) on manual systems, are utilized to determine the moding of the following features: Blower Mode (Bi-level, floor, Defrost, Recirc and rear Defrost. These features as determined by the OAT/IAT during activation sequence are maintained for the duration of engine run time. Class 2 supplies the ambient temperature. Calibratable temperatures are utilized to provide low, mid and high temperature ranges for feature selectable. Blower and mode have the range to select any valid feature positions. When the remote start active serial data is received ignition-off loop HVAC algorithms will act the same as if a run power mode received (i.e. re-calibration, After blow, ignition-off motor positioning etc.) off timer and ignition on timer have the functionality as in Run mode.

Remote Start De-activation

When the remote start is exited (class 2 power mode = run mode or remote start engine), all displays will revert to that based on actual settings on the vehicle. In the case of manual settings, displays will revert to actual state of operation of the features on the basis of their normal control algorithms.

Air Temperature Description and Operation

The air temperature controls are divided into three primary areas

1. Automatic operation
2. The heating and air conditioning system
3. The air conditioning (A/C) cycle

HVAC Control Module

The HVAC control module is a class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The body control module (BCM), which is the vehicle power mode master, provides a device on signal. The control module supports the following features

Air Temperature Description and Operation

Personalization

The HVAC control module will receive information that defines the current driver of the vehicle from the driver door module (DDM) through class 2 communication. The HVAC system will memorize the following system configurations for up to three unique drivers

1. Driver set temperature
2. Passenger set temperature
3. Mode
4. Blower motor speed (auto, speed 1, 2, 3, 4, 5, 6)
5. Air conditioning (A/C) compressor request, auto ON or A/C OFF

This information shall be stored inside the HVAC control module memory. When a different driver identification button is selected the HVAC control module will recall the appropriate driver settings. When the HVAC control module is first turned on, the last stored settings for the current driver will be activated except for the rear defrost and heated seat settings.

Air Temperature Actuators

The air temperature actuator is a 2-wire bi-directional electric motor. Two control circuits enable the actuator to operate. The control circuits use either a 0 or 12-volt value to co-ordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 12 volts. In order to move the actuator, the HVAC control module grounds the appropriate control circuit for the commanded direction. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction.

The HVAC control module determines the door position by counting motor pulses on one of the control circuits. These pulses are small voltage fluctuations that occur when the brush is shorted across two commutator contacts as the motor rotates. As the actuator shaft rotates, the HVAC control module monitors the voltage drop across an internal resistance to detect the pulses. The HVAC control module converts the pulses to counts with a range of 0-255 counts. The HVAC control module uses a range of 0-255 counts to index the actuator position.

Air Temperature Sensors

The air temperature sensors are 2-wire negative temperature co-efficient thermistors. The vehicle uses the following air temperature sensors

1. Outside
2. Inside
3. Upper right
4. Upper left
5. Lower right
6. Lower left

The upper and lower duct sensors are divided into left and right zone operation. The left side upper and lower duct sensors will only effect the operation of the left air temperature actuator and the right side upper and lower duct sensors will only effect the operation of the right air temperature actuator. The duct sensors are used to measure the temperature of the air exiting the ducts. The sensors operate within a temperature range between -6.5-57.5°C (20.3-135.5°F). When temperature increases the sensor signal decreases. The HVAC control module converts the 0-5 volt sensor signal to a range between 0-255 counts. If the HVAC control module detects that one of the duct temperatures must change, the HVAC control module will adjust the appropriate air temperature actuator. The following list shows the duct sensors that are monitored by the HVAC control module in each mode position

Air Temperature Description and Operation

If the HVAC control module detects a malfunctioning sensor, the HVAC system will only malfunction when the sensor is monitored.

The inside temperature sensor operates within a temperature range between -6.5-57.5°C (20.3-135.5°F). If the sensor is shorted to ground, an open or shorted to voltage, the HVAC system will use a default value.

The outside temperature sensor operates within a temperature range between -30-51°C (-22-123.8°F). The radio displays the OAT value that it receives from the HVAC control module through a class 2 message. If the HVAC control module has determined that the outside temperature sensor has failed, the radio shall display, 75, in place of the outside air temperature. If the sensor is shorted to ground, an open or shorted voltage, the HVAC control module will use a default value.

The radio displays the outside air temperature value that it receives from the HVAC control module through a class 2 message. The scan tool has the ability to update the displayed ambient air temperature. The outside air temperature value is displayed or updated under the following conditions

Air Temperature Description and Operation

Sunload Sensor

The sunload sensor is a 2-wire photo diode. The vehicle uses left and right sunload sensors. The 2 sensors are integrated into the sunload sensor assembly along with the ambient light sensor. Low reference and signal circuits enable the sensor to operate. As the sunload increases, the sensor signal decreases. 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 sensor is open or shorted, no sunload condition occurs.

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 prevents the A/C system from operating when an excessively high or low pressure condition exists. The engine control module (ECM) disables the compressor clutch under the following conditions

1. A/C pressure is more than 2850 kPa (413 psi). The clutch will be enabled after the pressure decreases to less than 2100 kPa (254 psi).
2. A/C pressure is less than 204 kPa (30 psi). The clutch will be enabled after the pressure increases to more than 220 kPa (32 psi).

If the ECM detects a failure in the A/C refrigerant pressure sensor or circuit, the class 2 message sent to the HVAC control module will be invalid. The HVAC control module will display A/C OFF on the module as long as the condition is present.

Heating and A/C Operation

The purpose of the heating and air conditioning (A/C) system is to provide the following

1. Heated air
2. Cooled air
3. Remove humidity from the interior of the vehicle
4. Reduce windshield fogging

Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve a desired temperature

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

The HVAC control module commands or monitors the following actions when an air temperature setting is selected.

WARMEST POSITION-The air temperature actuator door position directs maximum air flow through the heater core.

COLDEST POSITION-The air temperature actuator door position directs maximum air flow around the heater core.

BETWEEN THE WARMEST AND COLDEST POSITION-The following sensors are monitored to direct the appropriate amount of air through the heater core to achieve the desired temperature

1. Sunload
2. Outside temperature
3. Inside temperature
4. Duct temperatures

The A/C system is engaged by selecting any switch on the HVAC control module except the, A/C OFF switch. The A/C switch will illuminate, A/C OFF, when the A/C switch is selected. The HVAC control module sends a class 2 A/C request message to the body control module (BCM) for A/C compressor clutch operation. The BCM must communicate with the engine control module (ECM) in order for the A/C clutch to be engaged. The HVAC system uses a compact variable swash plate compressor. The following conditions must be met in order for the ECM to turn ON the compressor clutch from the HVAC control module request

1. The BCM will allow A/C operation if the following limits are within normal operating range A/C line pressure A/C refrigerant low temperature Ambient temperature Engine coolant temperature Battery voltage
2. HVAC control module OAT temperature more than 1.5°C (35°F) Control module operating range 9 and 16 volts
3. ECM Engine coolant temperature (ECT) is less than 128°C (262°F) Engine RPM is more than 0 RPM A/C pressure is between 2 850 kPa (413 psi) and 204 kPa (30 psi).

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

1. Throttle position is 100 percent
2. A/C pressure is more than 2 850 kPa (413 psi)
3. A/C pressure is less than 204 kPa (30 psi)
4. ECT is more than 128°C (262°F)

If there is a malfunction in the A/C system, the driver information center will read, SERVICE A/C SYSTEM, to alert the driver.

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

Dual Zone Operation

The HVAC control module has temperature settings for the driver and the passenger. If the passenger setting is turned off then the driver setting controls both driver and passenger temperature actuators. The passenger setting can not be used without the driver setting also being ON. The passenger setting can be turned ON or OFF by pressing the temperature switch on the passenger side of the HVAC control module. When the passenger setting is ON, the passenger temperature can be adjusted independently from the driver setting and the passenger temperature is displayed on the passenger side of the control module. A different sunload or duct temperature on one side of the vehicle may cause different discharge air temperatures even when the passenger setting is not turned ON.

Automatic Operation

In automatic operation, the HVAC control module will maintain the comfort level inside of the vehicle by controlling the air conditioning (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 60 or 90 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 adjust to maintain the temperature selected, except in the extreme temperature positions. The HVAC control module performs the following functions to maintain the desired air temperature

1. Regulate blower motor speed
2. Position the air temperature actuator
3. Position the mode actuator
4. Position the recirculation actuator

When the warmest position is selected in automatic operation the blower speed, based on coolant temperature, will increase gradually until the vehicle reaches normal operating temperature. When normal operating temperature is reached the blower will stay on high speed and the air temperature actuators will stay in the full heat position. When the coldest position is selected in automatic operation the blower will stay on high and the air temperature actuators will stay in the full cold position.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. The vehicle operator can select an extreme temperature setting but the system will not warm the vehicle any faster. In warm temperatures, the automatic HVAC system will also provide air conditioning in the most efficient manner. Selecting an extreme cool temperature will not cool the vehicle any faster.

The following describes the HVAC control head functionality upon receiving the remote start active serial data message and a power mode status is set to off a wake. Outside ambient temperature sensor, OAT- on automatic systems or intake air temperature (IAT) on manual systems, are utilized to determine the moding of the following features: Blower Mode (Bi-level, floor, Defrost, Recirc and rear Defrost. These features as determined by the OAT/IAT during activation sequence are maintained for the duration of engine run time. Class 2 supplies the ambient temperature. Calibratable temperatures are utilized to provide low, mid and high temperature ranges for feature selectable. Blower and mode have the range to select any valid feature positions. When the remote start active serial data is received ignition-off loop HVAC algorithms will act the same as if a run power mode received (i.e. re-calibration, after blow, ignition-off motor positioning etc.) off timer and ignition on timer have the functionality as in Run mode.

When the remote start is exited (class 2 power mode = run mode or remote start engine) all displays will revert to that based on actual settings on the vehicle. In the case of manual settings, displays will revert to actual state of operation of the features on the basis of their normal control algorithms.

Engine Coolant

Engine coolant is the key element of the heating system. The engine thermostat controls the normal engine operating coolant temperature. Coolant pumped out of the engine enters the heater core through the inlet heater hose. The air flowing through the HVAC module absorbs the heat of the coolant flowing through the heater core. The coolant then exits the heater core through the heater outlet hose and returns back to the engine block.

Special Tools

Special Tools Illustration Tool Number/Description J 43600 ACR 2000 Air Conditioning Service Center

Scheme 11

See also:
• Diagnostic System Check - Vehicle
• Testing for Intermittent Conditions and Poor Connections
• Circuit Testing
• Wiring Repairs
• Connector Repairs
• Control Module References
• Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
• Checking Aftermarket Accessories
• Noise Diagnosis - Blower Motor
• Noise Diagnosis - Air Conditioning (A/C) System
• Odor Diagnosis
• Engine Overheating (LY7)
• Blower Motor Malfunction
• Diagnostic Trouble Code (DTC) List - Vehicle
• Trim Plate Replacement - Instrument Panel (I/P) Lower (w/Floor Console)
• Fastener Notice
• Radio Replacement
• Radiator Air Baffle and Deflector Replacement - Upper
• Fastener Tightening Specifications
• DTC B0159, B0164, B0174, B0179, B0510 or B0515
• HVAC Connector End Views
• Air Delivery Description and Operation
• Air Temperature Description and Operation
• HVAC Compressor Clutch Does Not Disengage
• Blower Motor Always On
• Blower Motor Inoperative
• Sensor Resistance Table
• Re-Calibrating Actuators
• Fastener Tightening Specifications