Compressor Controls

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, and also allows the A/C load to be removed from the engine when needed.

Operation of the Compressor depends on the particular mode selected by the driver. When the A/C Mode Selector is in MAX, NORM, B/L, or DEF, battery voltage is applied through the HTR-A/C Fuse and Heater-A/C Compressor Control Relay to the remaining circuits.

The A/C sensor provides a variable voltage input to pin B6, C2 of the ECM. This input will vary depending upon the pressure in the A/C refrigeration system. Normal operation pressure range is between 30 to 420 psig.

The A/C Compressor Control Relay is operated by the ECM. The Relay contacts are normally open. When A/C Mode MAX, NORM, B/L or DEF is selected, an A/C on voltage is applied to terminal D9, of Connector C1, of the ECM. This signals the ECM to ground terminal C12, of Connector C1, energizing the Relay. The A/C Compressor Control Relay contacts close and provide voltage to the A/C Compressor Clutch.

When A/C pressure drops below 30 psig or exceeds 420 psig the ECM will remove the ground at C1/C12 to de-energize the Relay when the air conditioning load should be removed from the engine, such as during wide open throttle.