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.

Keep in mind:

• Some vehicles have one electric cooling fan while others have two. One cooling fan resistor controls the fan speed of both fans if so equipped.
• The cooling fan can start to run or continue to run after the engine is turned off. Take caution when looking under the hood even with the engine off.

How it's done:

• The cooling fan resistor is verified that it needs to be replaced. The battery is disconnected and both the battery and tray are removed.
• The defective cooling fan resistor is disconnected, unbolted from the frame, and removed.
• The new cooling fan resistor is installed, secured to the frame, and connected.
• The battery tray and battery are reinstalled and the battery is reconnected.
• The vehicle is tested to ensure proper operation of the cooling fan resistor.

Our recommendation:

The cooling fan resistor doesn’t require regular maintenance. If you suspect issues with your cooling fan, have one of our expert technicians diagnose and repair it. If the cooling fan is being replaced, it would be prudent to replace the resistor at the same time.

What common symptoms indicate you may need to replace the Cooling Fan Resistor?

• Cooling fan never stops running even with the ignition off
• Cooling fan never kicks in and engine temperature increases abnormally

How important is this service?

The engine will not run optimally if the temperature is too hot or too cold. You run the risk of overheating the engine if the cooling fan will not run at all, which could result in additional, costly repairs. Have the cooling fan resistor replaced as soon as it fails.