Compressor Clutch Diode HVAC: Description and Operation

When the ignition switch is in ON (II), voltage is applied to the coils of the radiator fan relay and the condenser fan relay (with A/C) through fuse 17. Whenever a ground is provided to the radiator fan relay and condenser fan relay, the relays are energized, turning ON the radiator fan motor and condenser fan motor. The relays can be grounded by the engine coolant temperature switch, Engine Control Module (ECM) (USA), or the A/C and heater fan switches via the A/C pressure switch and the A/C thermostat.

This diode prevents the engine coolant temperature switch from grounding the "A/C ON" input to the ECM.