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.


From the A/C Control Head, voltage is applied to the A/C Compressor Clutch through the Pressure Cycling Switch and the A/C High Pressure Switch. The Pressure Cycling Switch is normally closed but 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 if refrigerant pressure rises to a point that is too high for normal operation.

When voltage is applied to the A/C Compressor Clutch, it is also applied to the ECM at terminal C9 of connector C2. The ECM will then increase the engine idle speed while the A/C Compressor Clutch is engaged.