The purpose of the cooling fan relay is to pull air through the A/C condenser and the radiator. Most vehicles have two fans, one for the radiator and one for the condenser. Once you turn on the air conditioning, both fans should come on. The fan turns on when the power control module (PCM) receives a signal that the temperature of the engine needs extra air flow to cool it down.
The PCM sends a signal for the cooling fan relay to provide power to the cooling fan. The fan relay provides power via a switch, and sends 12-volts to the cooling fan which starts the operation. After the engine reaches a certain temperature, the cooling fan is turned off.
If the cooling fan relay is going bad, it can continue to run even when the ignition is off, or when the engine is cold. On the opposite side, the fan may not operate at all which will cause the engine to overheat or the temperature gauge to rise. If you notice your air conditioning is not working properly or your vehicle is constantly overheating, it may be time for your cooling fan relay to be replaced.
The cooling fan circuit normally consists of a relay, fan motor, and a control module. The cooling fan relay is the part that fails most often, so it should be tested by a professional if you are suspecting it is going bad. The mechanic will make sure it has the appropriate amount of power and ground connection by testing the circuit. If resistance is high on the coil, this means the relay is failing. If there is no resistance on the coil, the cooling fan relay has completely failed.
Since these can go bad over time, you should be aware of the symptoms that indicate the cooling fan relay needs to be replaced.
Signs that indicate your cooling fan relay needs to be replaced include:
- The cooling fan continues to run, even when the vehicle is turned off
- The air conditioning is not working properly, either it is not cool or does not work at all
- The vehicle constantly overheats or the temperature gauge reads higher than normal
If you are noticing any of the above issues, you just might have a problem with your cooling fan relay. If you would like this have this issue checked, contact a certified mechanic to inspect your vehicle and make any repairs as necessary.
This article originally appeared on YourMechanic.com as How Long Does a Cooling Fan Relay Last? and was authored by Valerie Johnston.