Powertrain Control Module (PCM)

WARNING: This page is about a different car, the 1996 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.

Based on signals from various sensors, PCM controls A/C compressor clutch operation through A/C compressor relay. To enable A/C compressor relay, PCM will provide a ground path. PCM will enable A/C compressor clutch operation whenever the engine is running and there is a request for A/C operation. PCM will disable A/C compressor clutch operation:

During wide open throttle (greater than 90 percent).
When A/C head pressure is greater than approximately 414 psi (29.1 kg/cm² ). Reference voltage will be approximately 4.27 volts.
When A/C head pressure is less than approximately 34 (2.4 kg/cm² ). Reference voltage will be approximately .35 volt.
When ignition voltage is less than 10.5 volts.
When engine speed is greater than 4500 RPM for 5 seconds or 5400 RPM.
When engine coolant temperature is greater than 257°F (125°C).
When intake air temperature is less than 41°F (5°C).