Compressor HVAC: Description and Operation

CIRCUIT OPERATION
The A/C Compressor for the Air Conditioning System is belt-driven by the engine through the A/C Compressor 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 necessary.

Operation of the compressor depends on the particular A/C mode selected by the driver. When the A/C Mode Selector is in MAX, NORM, HI-LEVEL or DEF, battery voltage is applied through Fuse 8 and the Heater and A/C Control Assembly Selector to the A/C Compressor Control Relay.

DESCRIPTION
The path to the A/C Compressor Control Relay is through the A/C Low Pressure Switch and the A/C High Pressure Switch, which are both normally closed. The A/C Low Pressure Switch opens if the refrigerant charge is too low for operation of the A/C Compressor Clutch without possible damage to it. The A/C High Pressure Switch opens when refrigerant pressure is too high for normal operation.

The A/C Compressor Control Relay is operated by the Electronic Control Module (ECM). When the ECM receives the A/C On signal (battery voltage) at terminal C2/2, the ECM grounds terminal C1/3, which energizes the relay. When the A/C Compressor Control Relay is energized, voltage is applied to the A/C Compressor Clutch through the contacts of the relay. If the ECM determines that the A/C load should be reduced, such as during full throttle, the ECM de-energizes the A/C Compressor Control Relay. This removes voltage from the A/C Compressor Clutch and removes the A/C load from the engine.