Manual Climate Controls

DESCRIPTION

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 disengaged when air conditioning is not required or to remove the air conditioning load from the engine when needed.

OPERATION

Operation of the Compressor depends on the particular A/C Mode selected. When the A/C Mode Selector Switch is in MAX, NORM, BI-LEVEL or DEF, battery voltage is applied through Fuse 7 and A/C Control Head Selector Switch to the A/C Cut-Out Relay.

The current 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 low enough that freezing of the evaporator may take place (175 kPa/25 PSI). It closes again when the refrigerant pressure rises enough that additional cooling is required. In this way the A/C Compressor is cycled on and off to maintain the evaporator at a low temperature in the evaporator without allowing condensation to freeze.

The A/C High Pressure Cut-Out Switch is normally closed. It opens to disengage the A/C Compressor Clutch when refrigerant pressure becomes too high for normal operation.

The A/C Cut-Out Relay is operated by the Engine Control Module (ECM). When the ECM receives the A/C ON signal the ECM grounds the A/C Cut-Out Relay, energizing the relay. When the Relay is energized, voltage is applied to the A/C Compressor Clutch through the closed contacts of the relay

If the ECM determines that the 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 current resulting from the voltage spikes. The voltage spikes are generated by the collapsing magnetic field of the clutch coil each time the clutch is de-energized.