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


Old 12-08-16, 10:50 AM
Thread Starter
Join Date: Mar 2010
Posts: 6
Received 0 Votes on 0 Posts
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?
Sponsored Links
Old 12-08-16, 11:53 AM
Join Date: Oct 2016
Posts: 1,294
Received 32 Votes on 29 Posts
Do the capacitors test ok? Are they correct for the motor? What is supply voltage to the motor?
Old 12-08-16, 02:33 PM
Join Date: Oct 2013
Location: United States
Posts: 2,698
Received 11 Votes on 11 Posts
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.
Old 12-08-16, 06:48 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 52,531
Received 330 Votes on 308 Posts
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

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes
Ask a Question
Question Title:
Your question will be posted in: