Automatic Climate Controls

DESCRIPTION

The A/C Compressor for the air conditioning system is belt-driven by the engine by way of the A/C COMPRESSOR CLUTCH. The Clutch allows the A/C Compressor to be disengaged when air conditioning is not required or when the air conditioning load should be removed from the engine, such as during full throttle.

OPERATION

Operation of the A/C Compressor depends on the particular A/C mode selected by the driver. When the IGNITION SWITCH is in RUN, battery voltage is applied to the coil and contacts of the A/C SELECT RELAY. The HEATER AND A/C CONTROL ASSEMBLY grounds the other side of the A/C SELECT RELAY coil when the A/C Compressor should operate. This will occur in the AUTO, BI-LEVEL and DEF modes, when the A/C Temperature setting is low enough to require A/C Compressor operation.

When the A/C SELECT RELAY is energized, voltage is applied to the contacts of the A/C CUT-OUT RELAY and the A/C ON input of the ELECTRONIC CONTROL MODULE (ECM).

The voltage path to the A/C CUT-OUT RELAY is through the PRESSURE CYCLING SWITCH and the A/C HIGH PRESSURE CUT-OUT SWITCH which are normally closed. The PRESSURE CYCLING SWITCH opens if the refrigerant pressure drops below 25 psi, which is the point where icing of the evaporator may take place. When refrigerant pressure rises again, the PRESSURE CYCLING SWITCH closes, re-engaging the A/C COMPRESSOR CLUTCH. In this way, the A/C Compressor is cycled on and off to maintain a low temperature in the evaporator without allowing condensation to freeze.

The A/C CUT-OUT RELAY is operated by the ECM. When the ECM receives the A/C ON signal, the ECM grounds terminal C15, energizing the relay. When the A/C CUT-OUT RELAY is energized, voltage is applied through the closed contacts of the relay to the A/C COMPRESSOR CLUTCH. The A/C HIGH PRESSURE CUT-OUT SWITCH opens to disengage the A/C COMPRESSOR CLUTCH when refrigerant pressure is too high for normal operation.

If the ECM determines that engine load should be reduced, such as during full throttle, the ECM de-energizes the A/C CUT-OUT RELAY, which removes voltage from the A/C COMPRESSOR CLUTCH, thus removing the A/C load from the engine.

The COMPRESSOR CLUTCH DIODE connected across the A/C COMPRESSOR CLUTCH provides a path for the induced voltage spikes which are generated each time the Clutch is turned off. The voltage spikes are generated by the collapsing magnetic field of the clutch coil.