Compressor HVAC: Description and Operation

With the A/C-Heater Select Control in any mode except VENT or HEAT, current flows from the HTR A/C Fuse through the Pressure Cycling Switch to the A/C Compressor Clutch and the NC Compressor operates. At the same time a signal is sent to the Engine Control Module (ECM). This A/C Request signal increases engine idle speed.

If the A/C system pressure drops below 25 psi, the A/C Low Pressure Cutout Switch opens, stopping current flow to the A/C Compressor. When the A/C system pressure rises to 45 psi, the switch closes and current again flows to the A/C Compressor.

If the A/C system pressure rises above 2,827-3,103 kPa (410-450 psi), the High Pressure Cutout Switch opens, disabling the Compressor Clutch. When the pressure drops below 2,827-3,103 kPa (410-450 psi), the switch closes and the Compressor Clutch re-engages.

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.