A/C Compressor Clutch

WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.

PCM regulates operation of A/C compressor clutch through a PCM-controlled A/C compressor clutch relay. This allows the PCM to disengage the A/C compressor when compressor load on engine may cause driveability problems (i.e., during hot restart, idle, low speed steering maneuvers and wide open throttle operation), or if A/C refrigerant pressure drops or rises beyond normal operating levels.

The A/C system can be engaged by pressing the A/C switch. The HVAC control assembly sends a A/C request message to the Body Control Module (BCM) which sends a class 2 message to the Powertrain Control Module (PCM). The A/C compressor clutch relay control switch in the PCM closes creating a ground and energizing the A/C compressor relay coil which closes the A/C compressor clutch relay switch energizing the A/C compressor clutch. The following conditions must be met for the PCM to turn on the compressor clutch:

BCM
- Battery voltage between 9-16 volts.
- A/C request from the HVAC control assembly.
PCM
- Engine Coolant Temperature (ECT) sensor parameter is more than 250°F (121°C).
- Engine RPM is below 5000 RPM.
- A/C Pressure is between 219-432 psi (1510-2979 kPa).
- Ambient temperature more than 38°F (3°C).
- Battery voltage between 9-16 volts.
- A/C request from the HVAC control assembly.

Once engaged, the compressor clutch will be disengaged for the following conditions:

Compressor thermal switch is opened.
Throttle position is 100 percent.
A/C Pressure is more than 432 psi (2979 kPa).
A/C Pressure is less than 27 psi (186 kPa).
Engine coolant temperature is more than 121°C (250°F).
Engine speed is more than 5500 RPM.
Transmission shift.
PCM detects excessive torque load.
PCM detects insufficient idle quality.
PCM detects a hard launch condition.

When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.

Refrigerant pressure sensing may be accomplished by monitoring high and low pressure switches or a pressure sensor which will register either high or low pressure levels. Power steering load is monitored through a power steering pressure switch. Hot restart is monitored through the coolant temperature sensor. For component application and related wiring, see appropriate article in AIR CONDITIONING & HEATING.