With 4L80E Automatic Transmission

A/C "ON" Signal:

Circuit and Test Description:
Turning "ON" the air conditioning supplies CKT 59 battery voltage to the A/C compressor clutch and to terminal "B12" of the PCM connector to increase and maintain idle speed.

The PCM does not control the A/C compressor clutch, therefore, if A/C does not function, refer to the A/C section for diagnosis of the system.

If A/C is operating properly and idle speed dips too low when the A/C compressor turns "ON" or flares too high when the A/C compressor turns "OFF", check for an open CKT 59 to the PCM. If circuits are OK, it is a faulty PCM connector terminal "B12" or PCM.