Compressor Controls Circuit

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:
^ Disengages when air conditioning is not requested
^ Disengages when the engine load must be reduced

The Instrument Panel Module (IPM) requests A/C compressor clutch engagement with the system operating in the following modes:
^ DEFOG
^ FRONT DEFROST
^ A/C

Under normal operating conditions, the following events occur:
^ The PCM supplies a ground to the A/C compressor control relay coil
^ The relay energizes
^ Voltage is supplied to the A/C compressor clutch through the relay center fuse
^ The A/C compressor clutch engages
^ The compressor runs

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.