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 cycle on and off during normal operation, disengage when air conditioning is not requested, or disengage when engine load must be reduced.

With the heater and A/C control mode selector knob in MAX A/C, NORM A/C, BI-LEVEL, DEFOG or DEFROST, battery voltage is applied to the powertrain control module (PCM). 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 the relay center fuse and the A/C compressor control relay contracts. 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 de-energize the A/C compressor control relay to disengage the compressor, even through the voltage signal from the heater and A/C control is still present.

The A/C compressor clutch diode, connected across the terminals of the A/C compressor clutch, 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 one occurs every time the coil is de-energized.