A/C Compressor Clutch: Notes

Ignition voltage is supplied directly to the A/C compressor clutch relay. The Engine Control Module (ECM) controls the relay by grounding the A/C clutch relay control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. The driver has a fault line which is monitored by the ECM. When the ECM is commanding a component ON, the voltage of the control circuit should be near zero volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, a DTC will set. The ECM will monitor the control circuit for the following:

• A short to ground.
• A short to voltage.
• An open circuit
• An open relay coil
• An internally shorted or excessively low resistance relay coil.

When the ECM detects any of the above malfunctions, a DTC is set and the affected driver is disabled. For component application and related wiring, see appropriate A/C COMPRESSOR CLUTCH CONTROLS article in AIR CONDITIONING & HEATING.