fan motor help needed

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Sep 19, 2006

Can someone help me diagnose why my fan now only works on high speed? It recently stopped working on low.
I don't know whether its the motor or the switch.
What can I check first? I have a multimeter.
Does someone know which wire that I can check that would tell the story?

thanks, jim

1975 fj40
In my case it was the switch, I pulled it out last weekend and checked it with my multi-meter. The high setting worked, the low was open. I took apart the switch and cleaned a bunch of junk off the contacts and it worked again. The same was true of my hazard switch.
Vagabond......Could be the switch...however with a 32 year old "40" you might need to look into the fan motor. I had trouble with my 73 rear heater only working off and on. I disassembled it and cleaned all the gunk off everything. I used a non mineral based cleaner. You don't want any oil based cleaner inside the motor. I used emery paper to clean up the commutator and cleaned out the grooves with a knife blade. The brushes were about 50% so I just made sure they made good contact. Result was about 60% more motor speed! Whole process took about an hour.
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Could also be the resistor that cuts the voltage down. But if your motor is weak (as in needing a cleaning as posted above) the reduced voltage of "low" may be too low to spin the motor. I bought a rear heater that was advertised as "locked up", but after cleaning, it runs like a top.:D


I agree with the resistor if its not working at all. Although cleaning does a world of wonder on these mature vehicles. (Thats correct wording in this day, right?) I would put a meter on the connections at the fan and see if you are getting voltage on high and low. Should tell the tale. Good Luck!!
My rear heater motor starts out fine but then over the course of 20 seconds winds to a halt and smoke kinda curls up from it... I've cleaned it off, done everything I can think of to get it going... All wiring is good (replaced or cleaned) and I cleaned the internals. Any ideas? Pics of working setups and motor internals? Oh, Painless wiring harness, where is the proper place to tap into the blower power, the switch itself or is my line running from the high power line on the blower good enough? The main blower works like a champ. Thanks!

Brian, did you clean the armature with a little emery cloth? Then I use the tip of a razor saw to clean in between the copper on the armature. You also don't want to over lube an electric motor. Are the brushes good?
If the fan spins pretty freely, I'd check the armature/brushes.


If you saw smoke, then the armature windings have overheated burning off the varnish. Time to look for a replacement. All the cleaning in the world won't put the smoke back in! ;)

I was thinking(hoping) that the smoke was from too much oil. You know, like your Lionel Train;)
Mark is right, if you burned the varnish off the armature:frown:

Ed, only you would think of the train connection! :lol:

Though I no longer have my train set I do have the transformer for it. It has served in many other capacities! :D

I have a fan motor I got in a box of junk off e-bay that had the exact same symptoms. It would run fine for about 10 seconds then smoke and stop.

When I tried to disassemble it, to see if it could be fixed, the little circuit board the brushes were mounted to, was so brittle from the over heating, it just broke apart.

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