Compressor HVAC: Description and Operation

CIRCUIT DESCRIPTION
With the A/C-Heater Select Control in any mode except VENT or HEAT, current flows from the HTR A/C Fuse, through the Low Charge Protection Switch to the A/C Cutout Relay terminal B and the Electronic Control Module (ECM).

The A/C Request signal to the ECM closes the A/C Cutout switch in the ECM providing a ground at terminal C of the A/C Cutout Relay. This allows current to flow from the GAGES Fuse to terminal A of the A/C Cutout Relay, energizing the relay. Current from the HTR A/C Fuse then flows through the relay to energize the A/C Compressor Clutch.

The A/C Request signal to the ECM also increases engine idle speed.

The A/C compressor can be turned off in one of three ways. Moving the Function Lever to the VENT or HEAT position on the A/C-Heater Select control stops the current flow to the system from the HTR A/C fuse.

If the A/C system pressure drops too low, the Low Charge Protection Switch will open stopping the current flow.

If, while turning the vehicle, power steering system pressure rises above 550 psi, the Power Steering Pressure Switch opens. This interrupts the ground signal to the ECM causing the A/C Cutout switch in the ECM to open, de-energizing the A/C Cutout relay. When the power steering system pressure drops below 550 psi, the Power Steering Pressure Switch closes and the A/C Compressor again starts operating.

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.