DTC P0646 A/C Clutch Relay Control Circuit Low: General Description

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 ECM. When A/C is requested, the Engine Control Module (ECM) 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 ECM delays grounding the relay circuit for a short time, so the ECM can adjust the engine idle speed for the additional load. The ECM 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