Normal Compressor On Time

When the vehicle is operating above 15 MPH, minimum compressor on time is controlled to 2-6 seconds before the BCM will allow compressor clutch engagement.

After the minimum on time has expired, the BCM will disengage the compressor clutch only if the low side temperature is below 30°F (-1°C). The BCM then waits for the low side temperature to reach between 45°F (7°C) and 50°F (10°C) when it cycles the compressor on again.

This cycle continues until either the ECM or the BCM disengage the clutch because a fault in the system or vehicle climate needs change.

The conditions for BCM compressor clutch disengagement are, A/C low pressure switch open, A/C low side temperature below 30°F (-1°C), A/C high side temperature above 199°F (93°C) coolant temperature above 259°F (126°C) or open or shorted A/C low side sensor circuit.

The conditions for ECM compressor clutch disengagement are, wide open throttle signal from the TPS, system over voltage, system under voltage or power steering cut-out switch open. Except for wide open throttle signal, all the above conditions will keep the compressor disengaged only as long as the condition exists. Under the wide open throttle signal, the ECM will disengage the compressor clutch for a maximum of 20 seconds.