Refrigerant Pressure Sensor / Switch: 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 13. 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.

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 (A/C switch ON, heater fans switch ON, engine coolant temperature switch open, and ECM fan control output not grounded) to the condenser and radiator fan relays, the relay will deenergize removing voltage from the condenser and radiator fan motors causing them to stop running.