Circuit Operation

COMPRESSOR CONTROLS

The Compressor for the Air Conditioning System is driven by the engine by means of a belt drive and the AC Compressor Clutch. The Clutch allows the Compressor to be disengaged when Air Conditioning is not required. Power to the AC Compressor Clutch is supplied by the HTR-AC Fuse.

AC Compressor Clutch Diode
The AC Compressor Clutch Diode is connected across the terminals of the AC 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.

AC-Heater Selector Switch
With the AC-Heater Selector Switch in any mode except VENT or HEAT, current flows from the HTR-AC Fuse, through the Low Pressure Switch, to the AC Control Relay terminal B and the Electronic Control Module (ECM).

AC Request signal
The AC Request signal to the ECM closes the AC Cutout Switch in the ECM providing a ground at terminal C of the AC Control Relay. This allows current to flow from the Gages Fuse to terminal A of the AC Control Relay, energizing the relay. Current from the HTR-AC Fuse then flows through the relay to energize the AC Compressor Clutch. The AC Request signal to the ECM also increases engine idle speed.

The AC Compressor can be turned off in one of three ways:
^ Moving the Function Lever to the VENT or HEAT position on the AC-Heater Selector Switch stops the current flow to the system from the HTR-AC fuse.

^ If the AC system pressure drops too low, the Low Pressure Switch will open stopping the current flow.

^ If, while turning the vehicle, power steering system pressure rises above 3792 kPa (550 psi), the Power Steering Pressure Switch opens. This interrupts the ground signal to the ECM causing the AC Cutout switch in the ECM to open de-energizing the AC Control Relay. When the power steering system pressure drops below 3792 kPa (550 psi), the Power Steering Pressure Switch closes and the AC Compressor again starts operating.