Engine Cooling Fan: Operation

The auxiliary cooling fan circuit consists of a coolant temperature sensor, a relay and the auxiliary fan. When the coolant sensor reaches a predetermined temperature, it closes the circuit to the relay coil, which energizes the relay, passing 12-volts to the auxiliary fan. When the coolant temperature decreases below the setpoint of the sensor, the circuit to the relay opens and 12-volt power to the auxiliary fan stops. The cooling fan only operates when the cooling fan is on, and the coolant temperature sensor is above the set temperature.