Powertrain Control Module (PCM)
WARNING: This page is about a different car, the 2001 Pontiac Bonneville and 2000 Pontiac Bonneville. However, it is still accessible from the selected car via links, so may be relevant.
The PCM controls power to the A/C compressor clutch through A/C compressor relay. When PCM receives an A/C request signal from the A/C-heater programmer, the PCM grounds coil circuit of the A/C compressor control relay. This energizes the A/C compressor control relay (the relay contacts close), providing power to the A/C compressor clutch. Under various engine operating conditions (such as wide open throttle), the PCM prevents compressor clutch engagement.