The compressor for the air conditioning system is belt-driven by the engine through the A/C compressor clutch. The clutch controls the compressor in the following ways:

The heater and A/C control communicates the mode selection to the instrument panel module over the keyboard display driver (KDD) data bus. This communication link is only used by the IPM and heater and A/C control.

The IPM requests A/C compressor clutch engagement with the system operating in the following modes:

Under normal operating conditions, the following events occur:

The PCM monitors A/C refrigerant line pressure and engine coolant temperature. This information is placed on the Class 2 communication link and is monitored by the DIM. The DIM looks at A/C line pressure, engine coolant temperature and battery voltage. The DIM will request A/C operation from the PCM if these parameters are within normal operation limits and the IPM is requesting A/C operation.

If the PCM determines that the engine load should be reduced, such as during full throttle conditions, the PCM will de-energize the A/C compressor control relay. This will disengage the compressor, even though the request for A/C compressor clutch engagement from the IPM is still present.

The A/C compressor clutch diode is connected across the A/C compressor clutch terminals. This diode provides a path for current resulting from voltage spikes. The collapsing magnetic field of the A/C compressor clutch coil generate these voltage spikes. Voltage spikes occur every time the coil is de-energized.