Operation CHARM: Car repair manuals for everyone.
Home >> Cadillac >> 2008 >> CTS AWD V6-3.6L >> Repair and Diagnosis >> Heating and Air Conditioning >> Testing and Inspection >> Symptom Related Diagnostic Procedures >> Diagnosis By Symptom - HVAC System - Automatic >> Air Conditioning Compressor Malfunction

Air Conditioning Compressor Malfunction



Air Conditioning Compressor Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview)provides an overview of each diagnostic category.



Diagnostic Fault Information






Circuit/System Description

When the A/C switch is pressed, the HVAC control module grounds the A/C request signal circuit. This input will request the ECM to ground the A/C compressor clutch relay control circuit, which will switch the A/C CMPRSR CLUTCH relay on. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch assembly.


Diagnostic Aids

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

* Battery voltage is between 9-18 volts
* Engine coolant temperature (ECT) is less than 123°C (253°F)
* Engine speed is greater than 600 RPM
* Engine speed is less than 4,760 RPM
* A/C high side pressure is between 2929-269 kPa (39-425 psi) Air Conditioning (A/C) System Performance Test (Initial Inspection and Diagnostic Overview)
* Throttle position is less than 100 percent
* Evaporator temperature is greater than 0°C (32°F)
* ECM does not detect excessive torque load
* ECM does not detect insufficient idle quality
* The ambient temperature is above 1°C (34°F)



Reference Information
Schematic Reference

HVAC Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Automatic HVAC Description and Operation (HVAC - Automatic)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning)for scan tool information


Circuit/System Verification

Engine running place the mode switch in the defrost position. The A/C compressor clutch should engage.

If the clutch does not engage refer to Air Conditioning (A/C) System Performance Test (Initial Inspection and Diagnostic Overview)



Circuit/System Testing

1. Ignition OFF, disconnect the A/C Relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 86 and ground.

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

3. Verify that a test lamp illuminates between the ignition circuit relay coil feed circuit terminal 85 and ground.

• If the test lamp does not illuminate, test the ignition circuit for a short to ground or a open/high resistance. If the circuit tests normal and ignition circuit fuse is open, test all components connected to the ignition circuit and replace as necessary.

4. Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or a open/high resistance. If the circuit tests normal and B+ circuit fuse is open, replace the A/C Clutch Relay.

5. Disconnect the harness connector at the A/C Clutch Coil.
6. Test for less than 1 ohm of resistance between the A/C Clutch Coil ground circuit terminal ground.

• If greater than 1 ohm, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the A/C Clutch Coil.
8. Connect a 10-amp fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87 of the A/C Clutch Relay. Verify the A/C Clutch Relay is activated.

• If the A/C Clutch Relay does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the A/C Clutch Relay.

9. Connect a test lamp between the coil side of the A/C Clutch Relay ignition circuit terminal 85 and the control circuit terminal 86.
10. Command the A/C Relay output function ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

• If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.


• If the test lamp is always OFF, test the control circuit for a short to voltage, or an open/high resistance. If the circuit tests normal, replace the ECM.

11. If all circuits test normal, replace the A/C Clutch Relay.



Component Testing


Relay Testing
1. Ignition OFF, disconnect the A/C Relay.
2. Test for 137 ohms across the relay coil terminals.

• If the resistance is not close to the specified range, replace the relay.

3. Test for infinite resistance between switch side of the relay

• If less than infinite resistance, replace the relay

4. Install a 20-amp fused jumper wire between the relay coil side and 12 volts. Install a jumper wire between relay the coil side and ground. Measure for less than 2 ohms of resistance between the relay switch side.

• If greater than 2 ohms, replace the relay.




Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Compressor Replacement (Service and Repair)
* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Control Module References (Programming and Relearning)for HVAC control module and ECM replacement, setup, and programming


pro multis · About Operation CHARM