Powertrain Control Module (PCM)
WARNING: This page is about a different car, the 1998 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 the coil circuit of the A/C compressor control relay. This energizes the A/C compressor control relay (the relay contacts close), allowing power to the A/C compressor clutch. Under various engine operating conditions (such as wide open throttle), the PCM prevents compressor clutch engagement.