For 1990-2009 cars

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 heater and A/C programmer applies battery voltage to the powertrain control module (PCM) with the system operating in the following modes:

• | DEFOG

• | FRONT DEFROST

• | A/C

Under normal operating conditions, the following events occur:

1. The PCM supplies a ground to the A/C compressor control relay coil
2. The relay energizes
3. Voltage is supplied to the A/C compressor clutch through the relay center fuse
4. The A/C compressor clutch engages
5. 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 voltage signal from the heater and A/C programmer 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.