Compressor Control

The compressor for the air conditioning system is belt-driven by the engine through the A/C compressor clutch. The clutch allows the compressor to be cycled on and off during normal operation, disengaged when air conditioning is not requested or disengaged when engine load must be reduced.

The HVAC programmer applies battery voltage to the Powertrain Control Module (PCM) with the system operating in DEFOG, FRONT DEFROST or if the A/C button is selected and both the A/C high-pressure cut-out switch and pressure switch closed. This voltage signal tells the PCM that A/C compressor operation is requested.

Under normal operating conditions, the PCM then grounds the A/C compressor control relay coil and the relay energizes. Voltage is applied to the A/C compressor clutch through relay center fuse 5 and the A/C compressor control relay contacts. The A/C compressor clutch engages and the compressor runs.

If the PCM determines that engine load should be reduced, such as during full throttle conditions, it will deenergize the A/C compressor control relay to disengage the compressor, even though the voltage signal from the HVAC programmer is still present.

The A/C compressor clutch diode, connected across the A/C compressor clutch terminals, provides a path for the current resulting from voltage spikes. The voltage spikes are generated by the collapsing magnetic field of the A/C compressor clutch coil, and occurs every time the coil is deenergized.

During the compressor ON cycle, any of the following PCM Diagnostic Trouble Codes (DTC) will force the PCM to disengage the clutch. Refer to Computers and Control Systems for diagnosis of these codes: Computers and Control Systems

DTC 0530 - A/C REFRIGERANT PRESSURE SENSOR CIRCUIT

^ If the value of the A/C pressure switch is outside of the sensor range, either too high or too low, then the PCM will set this DTC and disable the A/C compressor.

DTC 1654 - A/C RELAY CONTROL CIRCUIT

^ The PCM will set this DTC is an improper voltage level has been detected on the circuit which controls the A/C relay.