A/C Signal: Description and Operation

The A/C compressor control module provides an A/C idle-up signal to the Powertrain Control Module (PCM) when the A/C compressor clutch is in operation. The PCM uses the A/C idle-up signal in order to modify the engine idle speed. The PCM will signal the idle speed control motor to activate the ISC motor plunger in order to open the throttle plate. Opening the throttle plate slightly will increase the engine speed in order to prevent a rough idle or a stalling condition.