How the System Works

Battery voltage is supplied through fuse 34 to the A/C compressor clutch relay contacts at all times.

With the ignition switch in ON (II), voltage is applied to the coil of the A/C compressor clutch relay through fuse 8. When you push the A/C switch ON, and the heater fan switch is in position 1, 2, 3, or 4, a "ground" input is provided to the Engine Control Module (ECM) through the A/C thermostat and the A/C pressure switch.

The A/C compressor clutch relay is grounded by the Engine Control Module (ECM). When energized, the relay allows battery voltage to energize the compressor clutch coil which then engages the clutch.

The A/C ON indicator light comes ON when the A/C system is running.

A/C Pressure Switch
The A/C pressure switch is located in the condenser outlet line where refrigerant is in a high temperature/high pressure liquid state. The switch will sense abnormally high or low pressure, and open the circuit. This removes ground, and the compressor will stop running.