Turning ON air conditioning supplies an ignition voltage to the A/C compressor clutch and to the ECM. The ECM uses the A/C signal circuit.

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

If the A/C is operating properly and the 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 in the A/C signal circuit to the ECM. If the circuits are OK, check for a faulty ECM connector terminal or ECM.