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wood_furnace 12-03-2012 11:10 AM

Motor on fire
I replaced the motor on a wood furnace blower. It was an old( ~30 years) Fasco motor. The replacement indicated is a Fasco D-150.

I have a fan center with no labels. I think it is Honeywell R8239-AT72H.

I also have a Honeywell L4064 Fan limit switch (jumper removed).

The original problem was that the old motor would not run - it would just hum.

I ASSumed the motor was bad. I also wanted to use the variable speed motor so I installed a 3-way switch. I used the feed (Fan/Load) from the L4064 to feed the switch then connect one output to the black (high) wire to motor and the other output to the red (low) to the motor.

That is really all that i changed. Also had to add a 5uF/370 capacitor for the new motor.

I connected the white wire from the motor to the white back to service panel along with other whites. This is how the old motor was.

Instead of connecting the wire (fan/load) from the L4064 to the motor it now go through the 3-way switch.

When I applied power the motor hummed, crackled, then caught fire.

I checked the voltage from the 3-way swith and it is 110v on either lead depending on switch position and the other lead is 0 volts so it appears to me that the switch is working ok and not double feeding the motor.

What in this situation do you think could cause the motor the catch fire?

beenthere 12-03-2012 01:07 PM

What did you do with the third speed wire.

wood_furnace 12-03-2012 02:10 PM

I did nothing with it. Did NOT cap it. Just left it lay in the box.

wood_furnace 12-03-2012 02:11 PM

I did nothing with it. Did NOT cap it. Just left lay bare in the box.

yuri 12-03-2012 03:00 PM

Then it probably completed a circuit to ground. You will get an induced voltage ( around 100 volts) in unusued wires in a multispeed direct drive motor. Should have arced and blown the breaker. Do you have a 15 amp breaker/fuse? If larger then that could be the problem too as the motor could burn B4 a larger breaker trips. Sounds to me like you got voltage on the neutral wire or ground wire and something else is wrong or that bare wire sent voltage to the ground and backwards to the motor. Do you have electric elements as well as the wood stove? Post some pice of all the wires and the relays.

wood_furnace 12-03-2012 03:42 PM

Thank you! It never occured to me that there could be voltage on the unused wire coming back from the motor but it makes sense now that you made me think about it. Was really stupid to not cap the unused wire no matter what I "thought". It has a 20 amp breaker for some reason? There are no other electric compents involved - the wood furnace is compeltely isolated from everything else. I'll see if can get pics. I'm not too good with that stuff.

beenthere 12-03-2012 03:46 PM

The speed wires are all tapped into the same run winding. Just at different pints. So all speed taps are hot when the motor is energized.

wood_furnace 12-03-2012 03:56 PM

That makes so much sense now. Will the 3-way switch work to control the speed? There will be voltage going back to the switch too since the high and low are wired back to the 3-way but it doesn't seem like that will be an issue since one is open while the other is closed?

yuri 12-03-2012 04:09 PM

You need to have a 15 amp fuse or breaker or if you ever have a house fire then your insurance may be void. We need to see pics of that fan center. If it is what I think it is then you need to have 24 volts running thru the fan switch then back to G to energize the high speed and use the normally closed wire of that relay for your low speed and it should work OK. The relays on those fan centers can stick when they get old and you can energize both windings at the same time.

With that relay you take hot directly to the line of the furnace and use normally open for high speed and normally closed for low speed and take 24 volts ffrom the transformer run it thru the fan switch and back to G and it should work.

beenthere 12-03-2012 05:17 PM

It will work with the switch. The voltage on the wire that is not energized from the switch won't matter, since its on an isolated terminal.

wood_furnace 12-10-2012 08:31 AM

I installed a new motor yesterday(capped unused speed wire) and it works perfectly! Thanks for your help with this.

yuri 12-10-2012 08:49 AM

:yes:Yur Welcome.

veesubotee 12-10-2012 09:22 AM


Originally Posted by yuri (Post 1070146)
:yes:Yur Welcome.

I like that.

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