A/C Signal: Description and Operation

A/C Circuit:

PURPOSE
The air conditioning switch applies the battery voltage to the engine control module (ECM) when the air conditioning is turned ON. The ECM then decides--based on other inputs whether to activate the A/C Compressor clutch.

OPERATION
When the driver turns on the A/C system a voltage signal is supplied to the ECM (as an indication that the A/C system is needed) and to one side of the A/C relay coil located on the right fender apron relay box near the firewall.

The ECM determines if engine conditions are suitable for A/C operation (idle speed, ignition timing and air/fuel mixture). If the ECM senses that conditions are suitable for A/C operation it supplies the ground circuit for the A/C relay coil energizing it. This allows the relay to supply voltage to the compressor clutch.