Compressor HVAC: Description and Operation

A/C Compressor System Schematic, Early Production:

A/C Compressor Controls Schematic, Late Production:

DESCRIPTION AND 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 from the engine whenever air conditioning is not required.

The operation of the A/C Compressor Clutch is controlled by the Electronic Control Module (ECM) by grounding the 366 circuit at connector C3, terminal F4. This energizes the A/C Compressor Control Relay and voltage is applied to the A/C Compressor Clutch.

The Climate Control Panel (CCP) accepts input requests from the driver via the front panel push buttons. The input signals determine the operating mode for the Climate Control System and are sent to the Body Control Module (BCM) over a data line (Circuit 718). If the BCM senses that cooling is required, it will signal the Engine Control Module (ECM) to turn on the Compressor through a data line (Circuit 491).

The BCM cycles the Compressor on and off according to the temperature levels indicated by the A/C High Side and Low Side Temperature inputs. Should the refrigerant level drop to a point where further operation would damage the Compressor, the A/C Low Pressure Switch opens and the BCM signals the ECM to stop compressor operation.

The ECM also receives inputs which affect operation of the Compressor. The inputs are throttle position, coolant temperature, vehicle speed and power steering pressure.