Air Conditioning Compressor Malfunction LBW, LCD, LBX OR LBS

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.

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

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Manual HVAC Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

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.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Air Conditioning Compressor Malfunction LDE, LLU, 2H0 OR LDK

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.

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

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Manual HVAC Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

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. Activate and deactivate the A/C compressor with 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.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.