Compressor Clutch Relay: Description and Operation

Wiring Diagram.:

PURPOSE
In order to improve idle quality, and engine performance during wide open throttle, the A/C compressor operation is controlled by the ECM.


OPERATION
When the HVAC panel is switched to the A/C or Defrost position and the A/C system has adequate charge, an A/C request signal is sent to the ECM. When the A/C request signal is received by the ECM, the ECM will ground relay CKT 459 (A/C disable relay) long enough to adjust engine idle rpm. Once idle speed has been adjusted, the ECM will remove the ground from relay CKT 459, which will allow voltage to be applied to the A/C compressor clutch.

This means that the A/C compressor is normally engaged until the disable relay is energized to break the clutch engagement circuit.