I’ve had a couple of electric fans stop for what seemed like no reason at all, and all troubleshooting pointed to their having an open winding and probably not worth fixing. I decided to poke around some, and found that modern fans are “thermally protected” with a thermal fuse wired into the motor circuit. These thermal fuses open up when a set temperature is hit. It is very easy to hit this “over temperature” limit when there is even a slight drag on the motor, It seems that a lot of cheap fans must use fish oil as a lubricant, because I’ve seen a bunch that bound up for what must be no reason other than normal use.
So here’s what I know. Remember that it’s DANGEROUS messing with things like this. If you mess up, you could electrocute yourself or burn your house down. Is it worth it?
The fusing is on the common wire to the fan motor. On this one it was red, and the main wire that didn’t run through the switch. Follow it up, into the motor where it should split out to the starter capacitor. I think I’ve seen them on either side of the starter cap, but this one was right between the common wire and one of the cap leads, which was also red.
The TOUGH part is getting another thermal fuse, and successfully splicing it into the circuit. Thermal fuses are available at Radio Shack. The pointy or highlighted end of the fuse is the more sensitive part of the thermal fuse. Most of the other fans I’ve seen had crimps on the wire so that it wouldn’t accidentally get blown when being assembled. This one was soldered, so I used some large alligator clips to heat sink between the soldering and the fuse. Double check the fuse when you’re finished and slip the insulation back around the assembly.
THEN you have to get this mess bundled up, insulated and connected to the motor frame like it was before. NOT easy, and it could be a very bad thing if you mess up.