A/C Signal: Description and Operation

A/C IDLE-UP SIGNAL
The Air Conditioning (A/C) amplifier outputs an A/C idle-up signal to the Engine Control Module (ECM) when the A/C compressor clutch is in operation. The ECM will then send a signal to the Idle Speed Control (ISC) motor. This signal to the ISC motor will activate the plunger to open the throttle plate. As the throttle plate opens, the engine speed will increase slightly to prevent a rough idle or stalling condition.