Compressor Controls

The Compressor for the Air Conditioning System is driven by the Engine by means of a Belt Drive and the A/C Compressor Clutch. The Clutch allows the Compressor to be disengaged when the Air Conditioning is not required.

When the Ignition Switch is in RUN position, Battery voltage is supplied to the Heater and A/C Controls Selector Switch through HTR-A/C (Fuse 12) and BRN (141) wire. When one of the appropriate A/C functions is selected (MAX, NORM, BI-LEVEL, BLEND OR DEF.) an A/C Request signal is created by passing Battery Voltage to the Vehicle Control Module (VCM). The path for this request voltage is as follows: LT GRN (66) wire to the A/C High Pressure Cut-Off Switch, then DK GRN/WHT(762) wire to the VCM. The VCM also monitors the Low Pressure Switch in the System through the DK GRN (603) wire. If the pressure drops below a predetermined level, the VCM disables the A/C operation.

When the A/C Request Signal is generated, the VCM will produce an A/C Enable signal on the DK GRN/WHT (459) wire which will provide a ground for the A/C Enable Relay Coil. Battery Voltage is provided through PNK (639) wire from IGN-E Fuse and will cause a current flow through the Coil of the Relay and energize it. With the Relay contacts closed, Battery Voltage will be provided from A/C Comp Fuse to ORN (1240) wire through the Relay contacts, to DK ORN (59) wire and finally to the A/C Compressor Coil. The A/C Compressor Coil is grounded by BLK (850) wire. Current will flow causing the Clutch to engage.

The A/C Compressor Clutch Diode is connected across the A/C Compressor Coil Circuit. Whenever the Clutch is de-energized, the magnetic field around it collapses, generating an induced voltage in the Clutch Coil. The diode provides a path for the current resulting from the induced voltage so that other circuit components are not damaged.