GM Service Manual Online
For 1990-2009 cars only

In order to improve engine operation, and protect the A/C compressor and A/C clutch during Wide Open Throttle (WOT) performance, the A/C compressor operation is controlled by the PCM.

This A/C system consists of the following components:

    • The heater and A/C control
    • The A/C refrigerant pressure sensor
    • The A/C clutch relay
    • The A/C compressor clutch
    • The PCM.

When the heater and A/C control is placed in the A/C mode, a request signal is sent to the PCM. The PCM will then energize the A/C clutch relay, unless abnormally high or low A/C pressure is detected by the A/C refrigerant pressure sensor. The PCM will also turn the cooling fans ON when A/C is requested. The A/C clutch relay is controlled by the PCM so that the PCM can increase idle speed before turning ON the clutch or disable the clutch during WOT, or high coolant temperature.

The C60 A/C (manual controls) system utilizes a hard wire request circuit from the HVAC Programmer to the PCM to request A/C. The CJ2 A/C system (automatic controls) utilizes the serial data circuit to request A/C.

The PCM energizes the A/C clutch whenever the engine is running less than 4895 RPM and A/C has been requested, unless any of the following conditions are met:

    • Wide Open Throttle (WOT).
    • A/C head pressure greater than 410 psi or less than 0 psi (as determined by the A/C refrigerant pressure sensor).
    • Ignition voltage less than 10 volts.
    • Engine speed greater than 5594 RPM.
    • ECT greater than 125°C (257°F).

The A/C Request Table should be used for diagnosing the C60 A/C request circuit only. For CJ2 A/C systems, refer to HVAC for diagnosis. Refer to HVAC for diagnosing the refrigerant portion of the system.

The scan tool will be used in diagnosing the system. The PCM has the ability to display the following parameters:

    • A/C request input to the PCM
    • A/C compressor status
    • A/C system pressure
    • A/C clutch ON or OFF status