A/C Compressor Clutch Control Diagnosis

A/C Compressor Clutch Control Circuit Diagnosis (1 Of 3):

A/C Compressor Clutch Control Circuit Diagnosis (2 Of 3):

A/C Compressor Clutch Control Circuit Diagnosis (3 Of 3):

A/C Compressor Clutch Control:

Circuit Description
The Powertrain Control Module (PCM) receives the A/C request from the Instrument Panel Cluster (IPC) . When the A/C is requested the PCM provides a ground path to the A/C compressor relay circuit. When the A/C compressor relay control circuit is grounded the A/C compressor clutch relay energizes. After the A/C request has been selected, the PCM delays grounding the A/C compressor relay control circuit for 0.3 second. This allows the PCM to adjust the engine idle RPM for the additional load.

The PCM will temporarily de-energize the A/C compressor clutch relay for one or more of the following conditions:

^ A hot engine restart
^ A Wide Open Throttle (WOT) Throttle Position (TP) sensor over 90%.
^ Engine Speed is greater than 6000 RPM
^ An Idle Air Control (IAC) valve reset The A/C compressor clutch relay will remain de-energize when one or both of the following one or both of the following conditions exist:

- A DTC P0530 sets.
- An A/C request signal does not exist due to an open A/C select switch circuitry.

Refer to Heating and Air Conditioning for more information on the A/C refrigerant systems.

Diagnostic Aids
If the complaint is insufficient cooling, the problem may be caused by an inoperative cooling fan.

If a fan operates correctly, refer to Heating and Air Conditioning.

An A/C refrigerant pressure outside the range of 43 to 428 psi will cause the A/C compressor to be disabled by the PCM. Observe the A/C refrigerant pressure parameter on the scan tool for 2 minutes with the engine idling and the A/C on. If the pressure goes out of the range, refer to Heating and Air Conditioning in order to measure and diagnose.

Test Description
Number(s) below refer to number(s) on the diagnostic table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored on the scan tool for later reference.
3. The PCM will only energize the A/C relay when the engine is running. This test will determine if the relay or control circuit is faulty.
4. By disconnecting the relay, the system can be divided into two sections. If the clutch does not disengage, the fault lies on the compressor side of the system.
6. A test light that does not illuminate indicates that the A/C compressor clutch relay is faulty.
8. Determines if the system is normal or if the A/C refrigerant pressure sensor reading is out of range.
9. Determines if the signal is reaching the PCM from the A/C control panel through the IPC. The signal should only be present when an A/C mode or defrost mode has been selected.
16. The A/C request signal is communicated through the IPC to the PCM over the UART serial data line. The A/C selector switch must send a signal to the IPC before the IPC will send a signal to the PCM to turn ON the A/C compressor.
17. Replacement PCM's must be reprogrammed. Refer to latest Techline information for programming procedures.
21. This step determines if the A/C refrigerant pressure sensor is out of range causing the A/C compressor clutch to be disabled or if the A/C charge is to low to allow A/C operation.
24. Connecting circuit's 59 and 439 together bypasses the PCM's control of the A/C compressor clutch. An A/C compressor clutch that fails to engage at this point indicates that the fault is in circuit 59, the compressor coil or compressor coil ground circuit.
26. With the engine running and the A/C relay commanded ON, the PCM should ground the A/C relay control circuit. This will also illuminate the test light.
36. If no faults have been found at this point, refer to Diagnostic Aids for additional checks and information.