The A/C clutch relay is activated if the A/C switch is operated while the blower is running and system operation is enabled by the PCM. When A/C is requested, the Engine Control Module(PCM) provides a ground path to the A/C clutch relay control circuit. When the relay circuit is grounded, the A/C clutch relay is energized. The PCM delays grounding the relay circuit for a short time, so the PCM can adjust the engine idle speed for the additional load. The PCM will temporarily de-energized the A/C clutch relay for one or more of the following conditions:

- Full acceleration when the throttle is at WOT.(Wide Open Throttle)

- Risk of overheating: Engine coolant temp. exceeds threshold value

- A/C system pressure exceeds threshold value

- Engine starting

PCM sets DTC P0647 if the PCM detects signal higher than the possible range of a properly operating sensor.