BMW 735iL Cooling Fan Resistor Replacement at your home or office.

What is the Cooling Fan Resistor all about?

The cooling fan is designed to draw air through the radiator and air conditioning condenser to remove heat from the A/C refrigerant and the engine’s coolant. A direct drive, or belt driven fan, is mounted on a temperature-controlled clutch that draws air once the physical temperature at the fan is hot. An electric fan operates differently. When the engine temperature increases, the fans come on in stages, which are controlled by a resistor. When the engine is turned on, the temperature rapidly increases. The resistor is powered by the ignition and enables the cooling fan to run at slow speed. Once the engine reaches a manufacturer-predetermined temperature, a temperature switch indicates to the cooling fan resistor that the fan should run at high speed to draw more air through the radiator and provide extra cooling. If there is a second fan, its purpose is to provide even more airflow for the air conditioning and cooling system. When the air conditioning is turned on, the resistor supplies power to the second fan, which always runs at high speed.

Many cooling system fans will continue to run after the engine is turned off to rapidly drop the engine temperature. If the radiator fan resistor is shorted, one of the cooling fan modes may not work, the cooling fan may not turn off when the engine is cold, or the cooling fans may not come on at all.