GM Service Manual Online
For 1990-2009 cars only

A/C System

A/C operation is requested by the ACM using a serial data (Class 2) message to the PCM. The PCM will ground the A/C relay allowing current to flow through the A/C Compressor clutch coil. The PCM will disable or inhibit A/C compressor clutch operation during the following conditions:

    â€¢ High power steering load indicated
    â€¢ Engine not running
    â€¢ Engine at wide open throttle
    â€¢ Outside temperature below approximately 4°C (40°F)
    â€¢ Certain PCM DTCs set

The PCM will also engage the A/C compressor clutch during cranking in colder weather to prevent A/C slugging.