Blower motor still won't start after replacing motor and capacitor

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Old 12-08-16, 10:50 AM
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Blower motor still won't start after replacing motor and capacitor

I have an Air Flow (Lenox) AF80MPA100B4A gas furnace. The blower fan wasn't starting so I replaced it along with the capacitor. Exact same brand/model/etc. It started up fine but then later it wouldn't start again.

I found that I could get it to start if I gave the squirrel cage a push. This was late last night and it was getting cold so I set the fan to on so it would constantly run and I wouldn't have to worry about it stopping and then not restarting as it cycled throughout the night.

This morning when I woke up the fan had stopped and I heard the hum of it trying to start. I checked it again and it would still start and run with a push. I had an extra capacitor so I swapped those out but same behavior. I checked resistance on all three speed wires on the motor and they seem ok. It will start and run with a push in any speed so it doesn't seem like the motor.

I ruled out the thermostat by jumping the terminals on the control board. Same behavior as with the thermostat.

So unless there is something else that can have an effect here I either have two new but bad capacitors or a brand new but bad motor that still runs.

The only thing I can think of is that one of the capacitors is new but I've had it about a year and it was stored up in the attic by the furnace. I forgot I had that one which is why I bought the other one (which was off the shelf). So it does get hot up there but I don't see why it wouldn't store well in the same place it actually gets used.

Anything I could be missing?
 
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Old 12-08-16, 11:53 AM
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Do the capacitors test ok? Are they correct for the motor? What is supply voltage to the motor?
 
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Old 12-08-16, 02:33 PM
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You can try running the motor with an external power source. Plug into an outlet. If it comes right on your problem is elsewhere, if not it will eliminate any furnace component and narrows it to your motor or cap.
Hope this helps.
 
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Old 12-08-16, 06:48 PM
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The OEM blower motor is a 59M51. 1/2hp 120v 3 speed
The OEM run capacitor is a 53H06. 15uf @ 370vac

All three speeds are connected..... heat, cool and continuous (fan on).
If it won't stay running in at least one of the speeds the motor may have a problem.
Make sure it's turning the right direction. Air is blowing out the supply side.

Your manual...... USA Made AF80 Furnace Installation Instructions.pdf
 
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