A/C Clutch Circuit Diagnosis: Description

A/C clutch relay is controlled by Vehicle Control Module (VCM) to delay A/C clutch engagement after A/C is turned on. This allows VCM to adjust engine RPM before A/C clutch engages. VCM will engage A/C clutch any time A/C has been requested unless coolant temperature is high, A/C system pressure is low, A/C system pressure is high, wide open throttle, or high engine RPM.

When A/C-heater control panel is placed in A/C mode, a 12-volt signal is sent to VCM. When VCM receives this signal, VCM will ground A/C clutch relay control circuit to energize A/C relay. This is shown on scan tool as A/C REQUEST YES.

When an A/C request has been detected by VCM, VCM will ground A/C clutch relay control circuit. As a result, relay contacts close, allowing current to flow through relay to A/C compressor clutch. When A/C REQUEST has been detected by PCM, cooling fans will be turned on when A/C pressure is greater than a predetermined value.