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Electric Cooling Fan Problems Part 4

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.
» 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

Checking The Fan Motors

Once I've confirmed the fuses and fusible links are good, I go to the fan motors. Unplug one of the cooling fans, and referring to your vehicles wiring diagram, apply fused battery voltage to the positive side of the motor and ground the negative side. The motor should run. If not, the motor is bad and needs to be replaced.

Let me take a moment to talk about jumper wires. I have several kinds of jumper wires, but the one I use to supply battery power to a component is about eight feet long and has a large clamp on one end to clip on the positive battery post. About a foot from the clamp I have a fuse holder in line. Depending on what I am checking, I put the appropriate fuse in the holder to prevent potential damage to whatever I'm testing. And in case the end accidentally grounds I don't hurt anything. This is a very important safety feature and you should never run direct battery voltage to any component.

Now, back to our story. Some cars have a single cooling fan that runs at two speeds. In these cases, the connector may have:

  • Two terminals, one from a dual power feed through a dropping resistor, one for low speed and a resistor-bypass circuit for high speed, plus the second one for the ground. There's a splice or connector for the dual power feed earlier in the circuit. If you check by hot-wiring at the fan motor itself, it will run at high speed.
  • Three terminals (one for low-speed feed, one for high-speed and a common ground). Check each power feed terminal separately, using the common ground in each case.
  • Four terminals (high, low and two grounds). Hot-wire each pair separately with your jumper wires.
» Part 1       » Part 2       » Part 3       » Part 4
Part 5       » Part 6       » Part 7
Additional Information provided courtesy of and Warranty Direct
© 2000-2007 Vincent T. Ciulla

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