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Fan Motor on Furnace - won't stay on

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  • Fan Motor on Furnace - won't stay on

    I have an older furnace that I am trying to keep going for a little while longer until I can get a new one. I am having trouble keeping the fan running. Have been doing some home renovations and I think that the age of the furnace coupled with increased dust has caused some challenges for the furnace (even though I have been replacing filters). Anyways, the fan will stop working and will not even come on when I press the 'manual fan on' button - although I do hear a hum. I have taken the fan/motor out, spun it a little bit (appears to move very freely) and hooked it back up again. I have done this a couple of times and am usually successful in getting the fan to come on again. However, you do hear some squeeking noises periodically. After some time the fan will go off and can't get it back on again.

    Is there anything I can be looking at doing to the fan motor which might get it back on track for a short time - perhaps opening up and cleaning or replacing something?

    Any suggestions greatly appreciated. Thank you.

  • #2
    Re: Fan Motor on Furnace - won't stay on

    In your last post you said the motor seized. You cleaned it and it worked for a while longer. Now it no longer works again with occasional noise.

    Probable causes:

    - Bad bearings
    - bad windings
    - bad capacitor

    Most modern motors have sealed bearings. There is nothing you can jigger, oil, or tap to cause it to further run for any length of time. Excessive overheating of your heat exchanger can cause failure of the high limit switch, melting of parts, and cracking.

    Edited to reflect duplicate post.
    Last edited by Plumber Punky; 11-16-2012, 03:47 PM.

    ... it was plumbed by Ray Charles and his helper Stevie Wonder


    • #3
      Re: Fan Motor on Furnace - won't stay on

      I would check capacitor for proper capacitance. Also check amperage of motor during operation and compare to data plate. If motor is drawing more than its rating then it is likely no bueno. You mention alot of dust so I would also be looking for large accumulations of dust/gunk on the blower squirrel cage. I have seen the excessive weight of dust build up bog down a blower motor which, in turn, could cause limits to trip. If the unit was running unfiltered it could have several issues. Also check any airflow obstructions as the motor has to work extra hard (draw more amps and overheat) trying to pull return air through restricted vents.