Compressor HVAC: Description and Operation

CIRCUIT OPERATION:

The 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 Switch is in MAX, NORM, BI-LEVEL or DEF, battery voltage is applied through the HTR A/C Fuse and A/C Control Head to the remaining circuits.

For vehicles equipped with the V6 VIN T engine, the path to the A/C Compressor Control Relay is through the Pressure Cycling Switch and the A/C High Pressure Switch which are both normally closed. The Pressure Cycling Switch opens when the system low-side pressure is too low. This low pressure may be due to evaporator icing (normal operation), low ambient temperature or refrigerant discharge (abnormal condition). The Pressure Cycling Switch closes again when these conditions are corrected. This action causes the compressor to cycle on and off, under normal operation, to prevent icing. 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 ECM. When the ECM receives the A/C ON signal at terminal C9 of connector C2, it grounds terminal F1 of connector C3 energizing the relay. When the relay is energized, voltage is applied to the A/C Compressor Clutch through the contacts of the relay.

If the ECM determines that engine load should be reduced, such as during full throttle, the A/C Compressor Control Relay is de-energized, which removes voltage from the A/C Compressor Clutch, thus removing the A/C load from the engine. The Power Steering Switch monitors power steering load. When power steering demand is high the ECM will again de-energize the A/C Compressor Relay to reduce engine load.