Condenser Fan: Description and Operation

How the Circuit Works
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 radiator fan switch, engine or powertrain control module (ECM or PCM) (USA), or the A/C and heater fan switches via the A/C pressure switch and the A/C thermostat.

A/C Thermostat
The A/C thermostat is located on the evaporator housing. The A/C thermostat turns off the A/C compressor clutch if the temperature at the evaporator goes below 3 °C (37 °F). This prevents condensation from freezing on the evaporator fins and blocking the air delivery into the passenger compartment. If the temperature goes below 3 °C (37 °F) turning off the A/C thermostat, and the BLU/RED wire at the A/C diode was the only wire providing ground to the condenser and radiator fan relays (A/C switch on, heater fans switch on, radiator fan switch open, and ECM or PCM fan control output not grounded), the relay will deenergize removing voltage from the condenser and radiator fan motors causing them to stop 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 A/C switch turns off the A/C compressor clutch if it senses abnormally high or low pressure. If the A/C pressure switch opens, and the BLU/RED wire at the A/C diode was the only wire providing ground to the condenser and radiator fan relays (A/C switch on, heater fans switch on, radiator fan switch open, and ECM or PCM fan control output not grounded), the relay will deenergize removing voltage from the condenser and radiator fan motors causing them to stop running.

A/C Diode
This diode prevents the radiator fan switch from grounding the "A/C ON" input to the engine or powertrain control module (ECM or PCM).