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Discussion Starter · #1 ·
A week ago I woke up to an intermittent loud buzzing sound coming from my basement (2 seconds on/off). When I went down I could see that the blower fan wasn't turning and there was a burning smell.

Did some research and replaced the run capacitor, then turned it back on. The blower came right on and sounded great, except the speed was low. Took 2 hours to drop the temp 2 degrees. Then after that when the AC tried to kick back on I got the buzzing again, this time sustained (not intermittent), so I flipped the breaker, and took the blower out of the furnace. It's kind of nasty but spins pretty freely (see attached image).

My question is, is there any way that this motor does not need to be replaced? And if so should I get a new wheel too? I'm feeling pretty pessimistic about it at the moment. Thanks in advance.
 

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Discussion Starter · #3 ·
Hi Bitters. I definitely would like to do some testing before I shell out for a new motor. Do you have any suggestions?

I've made sure 120V is getting to the motor. I did some more digging this afternoon and did a test checking resistance between each of the four speed terminals of the motor and the common with the understanding that for a working motor the resistance should increase as speed decreases. Admittedly, my multimeter is not the best, but what I got was a constant 10 ohms for all four msmts.

Any other ideas or insights? I'm getting anxious and ready to pull the trigger on a replacement motor, but that's a good wad of dough ($240 is the cheapest I've found). Thanks as always.
 

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The capacitor is the correct size? You can also grab the shaft and see if there is any movement from side to side. It will move a little front to rear but shouldn't move side to side. If it does it could be dragging and time for a new motor. If this is the case and you are handy I have in the past actually taken motors apart and replaced sleeves/bearings for very little cost. I don't see people doing this anymore.
 

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Discussion Starter · #6 ·
The new capacitor is the same value and voltage rating as the old one and matches the specs on the motor. McGee, I checked the motor shaft, and there's no play either side to side or front to back. From what I can tell there's nothing mechanically wrong with the motor.

I did a thorough cleaning of the blower and replaced both air filters and tried to run it again. Once again it came up to speed smoothly and blew pretty well (still kinda weak), but after about 45 minutes of running and 2 degrees dropped it kicked off without reaching its setpoint. A few minutes later it tried to kick back on and made the same periodic buzzing as before.

Does anyone know if there is some kind of overheating protection built in to these circuits? It feels like it's tripping a fault and then is unable to restart. It's the only reason I can think of why it starts fine once but not the second time.

roughneck I'm still planning to try your suggestion of trying a different speed tap. Right now I'm waiting for the motor to cool down so it can start again. I'll let you know how it goes. Thanks for all the help and suggestions guys.
 

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You probably have a thermal cut out ( switch ) inside the motor that is turning the motor off when it gets too hot .

Be careful about reducing speed on the motor , at least long term . That can effect other things .

Do you have a Johnstone Supply of W W Granger near by ?

God bless
Wyr
 

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Discussion Starter · #8 ·
So I tried changing the cool terminal of my board to the medium-high speed tap of my motor this morning. The result was that the motor buzzed and wouldn't start at all, which is very strange since the high speed tap will usually start right up when the motor is cool.

I feel like it's pretty much time to replace the motor, but I want to know as confidently as possible that that will fix the problem. Are there any other problem sources that anyone can think of that would cause these issues other than motor failure?

WyrTwister, I have both Johnstone and Grainger in the city where I live.
 

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As far as our local stores , I much prefer Johnstone .

Motor and / or capacitor . A new motor may or may not come with a cap . And the new motor may or may not use the same cap as the old motor .

Caps are not normally very expensive .

God bless
Wyr
 

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Discussion Starter · #10 ·
Hi Wyr. Thanks for the recommendation. The cap is brand new, bought it last Friday. Even running a faulty motor surely it's still okay. I'll make sure and check the cap specs on my new motor if I get one.
 

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Discussion Starter · #11 ·
Got a replacement motor yesterday with a matched cap and installed it. It fired right up, but from my experience so far that's no guarantee of anything. However it stayed on, never overheated, and eventually reached the setpoint.

My one remaining concern is that air flow still seems weak, and it took about an hour and a half to drop 2 degrees. It seems like if the motor is running at speed (which seems like a fair assumption at this point) that it would have to be a problem with the ductwork or just a poorly spec'd hvac system for our home. Maybe I'm just being paranoid and overly sensitive. I'm probably gonna call this case closed for now, but any last bits of advice are welcome. Thanks for all the help guys.
 
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