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JTGizmo 03-11-2013 07:29 PM

Blower motor random stopping
 
Hello, I need some help with my furnace. When I came home today I could hear something happening from the furnace but the blower was not running. I took off the access cover and turned the heat back on manually , and nothing. I tried a little redneck logic and tapped the cage and it started. It worked for a bit and then...nothing, the blower is not even trying to start back. Once you let it set a while and turn it on it will start. The cage spins freely. So I assume i need to watch the input voltage to the motor when it stops. Then where should I check? The capacitor, the relay or the board... wiring? Is there a protective circuit in the motor that causes it to quit when it gets hot? I guess an overheat or short circuit is the culprit here

how 03-11-2013 08:37 PM

Check your heat tap on the board to see if the motor is being supplied with 120V when it should be.
Confirm that the motor wires are OK along with capacitor connections and the motor neutral connection on the board.
If your getting 120V at the heat tap, try a new capacitor with an equal rating.
If this doesn't fix it then it's time for a new motor.

old_squid 03-12-2013 09:52 AM

With ALL power to the furnace turned off, reach in and try to move the blower wheel up and down. If you get a noticable movement in any direction other than in and out the bearing(s) are more than likely worn and the motor needs to be replaced.

And yes, the motor has a built-in thermal cut out in case it gets too warm. With power supplied to the motor (and it not moving) all that electrical energy that now isn't being turned into mechanical energy gets turned into heat instead...... it's called locked rotor amps. Once the motor cools off the internal switch closes and the process starts all over again.

When the bearing first start getting bad an indication "usually is" that when the motor first starts up you'll hear what kind of sounds like an unbalanced starting noise. :whistling2: Hard to explain in words.

jagans 03-12-2013 10:01 AM

Did you persue that red neck logic and see if you had any loose connections, poorly soldered spade lugs etc? Was the intake end of the motor covered with dust and dirt so it could not cool itself? Do the simple things first. The fact that it started up when you jarred it points to either a loose connection of a fan that is hanging up on something. Make sure the set screw on the blower cage did not come loose and it is centered. Maybe a leaky Start cap too.


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