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