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Electric Cooling Fan Problems
It's not quite summer yet and I'm seeing cars come in with overheating problems. Here is how you can avoid coming into my shop with this problem.
More of this Feature
Part 1: Getting Hot Out
� Part 2: How They Work
Part 3: Now What?
Part 4: The Fan Motors
Part 5: Coolant Switch
Part 6: Coolant Sensor
Part 7: Cooling Fan Relay
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How It Works
The fan is powered by an electric motor, which is wired to a relay. The relay is a magnetically controlled switch. It typically has four terminals, two of which are current feeds from a fused source of 12-volt electricity. At the relay, there is one current feed into an electromagnetic coil, and one feed into a set of contacts for the switch, which is open. The other terminal for that open switch is connected to the electric motor for the fan. The fourth terminal, also for the coil, is wired to the PCM, which may look at various signals to determine whether or not to provide an electrical ground for that coil.

If, as in this circuit example, it gets a high-temperature signal from the coolant temperature sensor, also wired to it, the PCM can choose to ground the coil terminal. This energizes the coil, creating a magnetic field that pulls the arm on the power feed contact, so that it touches the terminal for the wire to the electric motor. That closes the switch of the relay. Current flows through the closed contacts of this switch to the electric motor, which spins to operate the fan.

Electric Cooling Fan Problems
Basic Cooling Fan Circuit

Next page> Now What? > Page 1, 2, 3, 4, 5, 6, 7

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© 2003 Vincent T. Ciulla


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