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
PCM monitors inputted voltage through A/C compressor relay. Checking voltage every 10 sec. under detecting condition, if the voltage lower than the specified value is detected for more than 5 sec., PCM sets P0646.
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Detects circuit short to low voltage | ● Poor connection ● Open or short to ground in A/C relay circuit ● Faulty A/C relay ● Faulty PCM |
Enable Conditions | ● After 0.5 sec under conditions below ● No DTC exists ● Engine works ● 11V ≤ Battery voltage ≤ 16V | |
Threshold value | ● Open or short to ground | |
Diagnosis Time | ● Continuous (More than 5 seconds failure for every 10 seconds test) | |
MIL On Condition | ● DTC only (NO MIL ON) |
Coil Resistance | 70Ω ~ 120Ω |
