Compressor HVAC: Description and Operation

Front A/C Unit
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 Powertrain Control Module (PCM) through the A/C thermostat and the A/C pressure switch.

The A/C compressor clutch relay is grounded by the PCM. 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.

Rear A/C Unit
With the ignition switch in ON (II), voltage is applied to the suction line solenoid valve and the transistor in the rear A/C unit switch. When you slide the rear A/C unit fan switch to LO, MED, HIGH, ground is provided to the suction line solenoid valve and to the "A/C ON" indicator light. The solenoid valve energizes and allows refrigerant to flow to the rear evaporator. When the front A/C unit switch (in the heater control panel) is ON, ground is provided to the transistor in the rear A/C unit switch. This allows current to flow through the transistor causing the "A/C ON" indicator light in the rear A/C unit to come on.