For 1990-2009 cars

## Air Conditioning Compressor Malfunction LDE, LLU, 2H0 or LDK

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
A/C Compressor Clutch Relay Coil Ignition | P0646 | P0645, P0646 | -- | --
A/C Compressor Clutch Relay Switch B+ | 1 | 1 | -- | --
A/C Compressor Clutch Relay Coil Control | P0646 | P0645, P0646 | P0647 | 3
A/C Compressor Control | 1 | 1 | 2 | --
A/C Compressor Ground | 1 | 1 | -- | --

1. A/C Compressor Inoperative
2. A/C Compressor Always ON
3. A/C Compressor Malfunction

### Circuit/System Description

When the A/C switch is pressed, the HVAC control module sends an A/C request message to the engine control module (ECM) via CAN-Bus. Therefore the ECM grounds the A/C compressor clutch relay control circuit, which will switch the A/C compressor clutch relay. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch. The A/C compressor clutch will be activated.

### Diagnostic Aids

The following conditions must be met in order for the ECM to turn on the A/C compressor clutch:

• | Battery voltage is between 9-18 V

• | Engine coolant temperature is less than 124°C (255°F)

• | Engine speed is greater than 600 RPM

• | Engine speed is less than 5 500 RPM

• | A/C high side pressure is between 269-2 929 kPa (39-425 PSI)

• | Throttle position is less than 100%

• | Evaporator temperature is greater than 3°C (38°F)

• | ECM does not detect immoderate torque load

• | ECM does not detect insufficient idle quality

• | The ambient temperature is above 1°C (34°F)

### Reference Information

#### Schematic Reference

HVAC Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Automatic HVAC Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

Note: Before executing Circuit/System Testing, all conditions shown in Diagnostic Aids must be met.

1. Ignition ON, activate and deactivate the A/C switch. Verify the scan tool A/C Switch parameter changes between Active and Inactive.

⇒ | If not the specified value, replace the A26 HVAC Control.

2. Activate and deactivate the A/C switch. Verify the engine control module (ECM) scan tool A/C Request Signal parameter changes between Active and Inactive.

⇒ | If not the specified value, replace the K33 HVAC Control Module.

3. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
4. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

5. Verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

⇒ | If the test lamp illuminates, test the control circuit for a short to voltage.

6. Ignition OFF, disconnect the harness connector at the Q2 A/C Compressor Clutch.
7. Test for less than 5 Ω between the Q2 A/C Compressor Clutch ground circuit terminal A and ground.

⇒ | If greater than the specified value, test the ground circuit for an open/high resistance.

8. Connect the harness connector at the Q2 A/C Compressor Clutch.
9. Ignition ON, connect a 10 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the Q2 A/C Compressor Clutch is activated.

⇒ | If the Q2 A/C Compressor Clutch does not activate, test the control circuit for an open/high resistance. If the circuit test normal, replace the Q2 A/C Compressor Clutch.

10. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
11. Command the engine control module (ECM) A/C Relay output function ON and OFF with the scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒ | If the test lamp always illuminates or always does not illuminate, replace the K20 Engine Control Module.

12. If all circuits test normal, replace the KR29 A/C Compressor Clutch Relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Air Conditioning Compressor Replacement

• | Heater and Air Conditioning Control Replacement

• | Control Module References for HVAC Control Module or Engine Control Module replacement, setup, and programming

## Air Conditioning Compressor Malfunction LBW, LCD, LBX or LBS

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
A/C Compressor B+ | B393B 04 | B393B 04 | -- | --
A/C Compressor Control | B393B 04 | B393B 04 | B393B 0B | 1
1. A/C Compressor Malfunction

### Circuit/System Description

The HVAC control module supplies battery voltage to the A/C compressor. When the A/C switch is pressed, the HVAC control module provides a pulse width modulation (PWM) signal to the A/C compressor in order to command the performance of the A/C compressor. The performance of the A/C compressor is regulated according to adjusted interior temperature on the basis of characteristic lines. Therefore the HVAC control module grounds the A/C compressor with the PWM signal.

### Diagnostic Aids

The following conditions must be met in order for the HVAC control module to turn on the A/C compressor:

• | Battery voltage is between 9-18 V

• | Engine coolant temperature is less than 124°C (255°F)

• | Engine speed is greater than 600 RPM

• | Engine speed is less than 5 500 RPM

• | A/C high side pressure is between 269-2 929 kPa (39-425 PSI)

• | Throttle position is less than 100%

• | Evaporator temperature is greater than 3°C (38°F)

• | ECM does not detect immoderate torque load

• | ECM does not detect insufficient idle quality

• | The ambient temperature is above 1°C (34°F)

### Reference Information

#### Schematic Reference

HVAC Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Automatic HVAC Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References

### Circuit/System Testing

Note: Before executing Circuit/System Testing, all conditions shown in Diagnostic Aids must be met.

1. Ignition ON, press and release the A/C Switch. Verify the scan tool A/C Switch parameter changes between Active and Inactive.

⇒ | If not the specified value, replace the A26 HVAC Control.

2. If all circuits test normal, replace the K33 HVAC Control Module and verify the Q46 Air Conditioning Compressor Valve can be activated and deactivated. If the Q46 Air Conditioning Compressor Valve cannot be activated or deactivated, replace the Q46 Air Conditioning Compressor Valve.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Air Conditioning Compressor Replacement

• | Heater and Air Conditioning Control Replacement

• | Control Module References for HVAC Control Module replacement, setup, and programming