The A/C relay is activated if the A/C switch is ON while the blower is running and system operation is enabled the ECM. Power is then supplied to the A/C compressor electromagnetic clutch and A/C system is operated. The A/C compressor is switched out to prevent it running when full engine output is required or there is a risk of overheating. The ECM also inhibits compressor operation on starting to permit running conditions to stabilize.
If there is Open in A/C control relay control circuit, ECM sets DTC P0645.
Item
Detecting Condition
Possible Cause
DTC Strategy
Circuit check, open
Poor connection
Open or short to ground in A/C relay circuit
Faulty ECM
Enable Conditions
-
Threshold Value
Open
Diagnostic Time
Continuous
MIL ON Condition
No MIL