Compressor Controls

CIRCUIT OPERATION
The compressor for the air conditioning system is belt driven by the engine through the Cornpressor Clutch. The clutch allows the compressor to be disengaged when air conditioning is not required or to remove the air conditioning load from the engine when needed.

A/C mode and compressor operation
Operation of the compressor depends on the particular A/C mode selected by the driver. When the A/C Mode Selector Switch is in MAX, NORM, BI-LEVEL or DEF, battery voltage is applied through the A/C Fuse and A/C Control Head Mode Selector Switch.

Compressor Control Relay
From the Heater and A/C Control Assembly, voltage is applied to the A/C Compressor Control Relay and Terminal J on Connector C2 of the ECM. On the V8 VIN Y engine the ECM will maintain the engine idle speed with the additional load of the A/C Compressor. On the V8 VIN 9 engine the idle speed is increased by the Fast idle Solenoid. Battery voltage at the A/C Compressor Control Relay is applied to the A/C Compressor Clutch through the normally closed contacts of the A/C Compressor Control Relay through the normally closed Pressure Cycling Switch.

Pressure Cycling Switch
The Pressure Cycling Switch opens when refrigerant pressure drops below 172 kPa (25 psi). it closes again when refrigerant pressure rises enough so that additional cooling is required. This action causes the A/C Compressor to cycle on and off so that evaporator temperature does not drop low enough to cause icing.

ECM and engine load
If the ECM determines that the engine load should be reduced, such as during wide open throttle, the A/C Compressor Control Relay is energized which opens the relay contacts removing voltage from the A/C Compressor Clutch.