Since the fan runs on any speed, the motor has to be okay. To run at full speed on speed number three is proper if you have a three-speed system. Most are four or five-speed systems or are continuously-variable through very unreliable computer controls. Which do you have?
When you have a normal common-sense fan speed switch with no computer controls, and only the highest speed works, that is usually caused indirectly by tight bearings in the motor. That drag causes the motor to draw higher-than-normal current, and that causes a thermal fuse in the resistor assembly to burn open. Replacing the resistor will restore normal operation on all speeds, but only until the fuse burns open again. Only the highest speed does not use the fused part of the resistor.
The total repair is to replace the motor, then the resistor assembly.
You can verify this problem by removing the fan motor, then running it while observing how it behaves. When turned off, the fan should coast to a stop over a period of three to five seconds. It should also spin freely by hand. When the bearings have become tight, the motor will stop almost instantly when it is turned off, and it will be fairly hard to turn by hand.
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Wednesday, December 20th, 2017 AT 2:54 PM
