Thursday, March 10, 2011

Electric Cooling Fans Cause Car Problems

I've seen quite a few electric cooling fans give up the ghost recently. The complaint from the driver is usually the air conditioning is not working. Although some owners may notice a car overheating condition. In either case, one of the first things that a mechanic will check is to verify that the electric cooling fan is running when it is supposed to be.
The overall efficiency of a car's cooling system is based on the amount of heat that can be removed from the cooling system and transferred to the air around it. At highway speeds ram air through the radiator is sufficient to maintain proper cooling.

 When the engine is idling or the vehicle is at very low speeds. The engine's cooling system needs additional airflow. On modern cars an electric cooling fan delivers this air.
The use of this type of fan eliminates the power drain during times when fan operation is not needed. Although there are vehicles still manufactured with belt driven fans, they are not as efficient or used as often as electric fan motors.
In most late-model applications electric fans save power and reduce the noise level of the vehicle. It's hard to say how long one of these units will last, because it depends on the vehicles operating conditions. Even though modern fans are well sealed they are still made with metal parts that can wear and corrode over time.
When I have one of these cooling fan motors to diagnose I will often go right for the source and check for power and a good ground at the motor itself. I have also seen mechanics take their power probe and supply 12 V to the fan motor to see if it runs. I have also seen and used the tap test where you just use the handle of a screwdriver to tap on the back of the electric motor.
Note that a qualified mechanic should conduct these tests. The cooling fan can be a dangerous car part. If a fan motor tests good then you will have to check the other side of the circuit. This consists of a cooling fan temperature switch and a fan relay.
The temperature switch could be located in a few different places. But often they are mounted near the thermostat. The coolant temperature switch is a simple on or off switch that sends power or ground to the cooling fan relay.
This should not be confused with the coolant temp sensor for the computer, which on many vehicles is separate. When the engine coolant is below 230° or so. The switch will remain open and the fan will not run. When the temperature switch senses the engine to be over 230° the switch closes. This energizes the coil in the relay, closing the contacts and sending 12 V power to the cooling fan motor.
The above is common example of a coolant fan motor circuit. Some vehicles may have more complicated systems. Some car makers will even use the ground side of the circuit to control operation of the fan.
Are you looking for more information on diagnosing automotive electrical problems? Mark has provided a helpful five-minute video that shows you how he uses wiring diagrams. Some vehicles have inherent problems in their cooling system. You can see Marks post about Taurus coolant leaks for more information.

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