Air Conditioning Compressor Malfunction
Air Conditioning Compressor Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
Diagnostic Fault Information
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 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 (HVAC - Automatic)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
Automatic HVAC Description and Operation (HVAC - Automatic)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning) 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 A20 Radio/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, remove 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 ohm 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 (Verification Tests) after completing the diagnostic procedure.
* Air Conditioning Compressor Replacement (LAF) (Removal and Replacement)Air Conditioning Compressor Replacement (LF1 or LFW) (Removal and Replacement)
* Radio Control Assembly Replacement (Radio Control Assembly Replacement)
* Control Module References (Programming and Relearning) for HVAC Control Module replacement, setup, and programming