Compressor HVAC: Description and Operation

COMPRESSOR CONTROLS
The Compressor for the Air Conditioning System is driven by the engine by means of a belt drive and the A/C Compressor Clutch. The Clutch allows the Compressor to be disengaged when Air Conditioning is not required.

Operation of the Compressor depends on the particular NC Mode selected at the Heater and NC Controller. When the Ignition Switch is in RUN, battery voltage is applied through the AC-HTR Fuse to the coil and contacts of the A/C Clutch Relay. With A/C ON selected, Terminal 966 of the Heater and A/C Controller is grounded which energizes the A/C Clutch Relay. The contacts of the Relay close and battery voltage is applied through the closed contacts and the normally closed A/C Accumulator Switch to the coil of the A/C Compressor Clutch. The coil is energized and the A/C Compressor Clutch engages.

If the refrigerant pressure drops to a point which may cause icing of the evaporator, the A/C Accumulator Switch opens, de-energizing the A/C Compressor Clutch. When the refrigerant pressure rises to a point where cooling is required again, the A/C Accumulator Switch closes to re-energize the A/C Compressor Clutch.

The A/C Compressor Clutch Diode is connected across the terminals of the A/C Compressor Clutch. Whenever the clutch is de-energized, the magnetic field around it collapses, generating an induced voltage in the clutch coil. The Diode provides a path for the current resulting from the induced voltage so that other circuit components are not damaged by it.