A/C outdoor Fan motor humming, replaced capacitor, still just humming


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Old 03-31-18, 01:20 PM
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Question A/C outdoor Fan motor humming, replaced capacitor, still just humming

My A/C is not working. The outdoor fan will occasionally spin up to very low RPM. But basically just sits an hums pretty loudly. Can't tell if it's the compressor and the fan, but think it's just the fan.

A bit of research tells me it's the capacitor.

Opening up my 15 year old unit showed the capacitor not visibly damaged, but there is also a "boost" capacitor" see attached picture

Ordered the exact same speced Cap from Amazon. Installed it today.
Amazon Capacitor




The unit is doing the exact same thing. Just humming. I disconnected the "Boost" Capacitor, thinking it may have gone bad. Didn't change anything. I disconnected the HERM side. The FAN still just hums. Also, I can spin the fan easily with a stick, so it's not frozen.

Any ideas? What's the likelihood the brand new Cap is bad? I have a standard digital multimeter (no microfarads though), is there a way to test the new CAP?

Thanks for any thoughts!
 
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Old 03-31-18, 01:26 PM
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Welcome to the forums.

If your new cap is performing identical to your old one.... the cap isn't the problem. The condensor fan motor takes a lot of abuse hanging out there in all weather. It sounds like the bearings may be worn out.
 
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Old 03-31-18, 01:46 PM
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Thanks Pete!

Anyway to test it with a multimeter, check the voltage or ohms while it's humming?

Any recommendations on where to get a replacement fan motor? It's a ~15 year old Trane Unit. See attached picture.



Also, any way I can check the health of the compressor motor easily? I think a guy put that "Boost" on there a few years ago and said the compressor needed hard start. Sounds like it was on it's last leg. Just like to know how much time is left on this thing if I spend much more $ on it.

Thanks for your helpful feedback. Help us guys more than you know.
 
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Old 03-31-18, 02:03 PM
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As compressors get older they have a harder time starting and a hard start cap gives them a boost. There really isn't any way of determining the life remaining in a compressor.

Post the model number of that condensor.
 
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Old 03-31-18, 03:43 PM
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I opened the top and checked the fan, I can't really spin it backwards, goes about 1/2 turn and stops. don't know if that's normal. It spins forward ok. The bearings don't sound great. I did hear the compressor fire up. So that's good news.

One thing I noticed was, the old Capacitor was a 45/7.5 which is what I replaced it with.

Looking at the fan motor. It is a 5 microfarad motor. I read different opinions if this may or may not be harmful having a mismatched CAP (Larger). What are your thoughts?


Here are the pics & model numbers. The unit is older than I thought.






Fan Motor



 
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Old 03-31-18, 11:25 PM
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https://www.amazon.com/GE-Trane-Cond...=TRANE+1%2F4HP

That is an expensive motor.

I would pop off that plastic rain shield and see if you also have the bolt holes for the larger universal 1/4hp motor.

( I doubt it )
 
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Old 04-02-18, 08:06 AM
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Thanks. I am going to check around today and see if I can find a replacement.
 
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Old 04-02-18, 08:20 AM
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Grainger the model replacement for $90.54
 
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Old 04-02-18, 03:20 PM
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Got the one from Grainger installed. Works like a champ. Mounting bolts fit. Had some problem getting the old fan blade off, it was rusted on there good. Took it to a machine shop. They took care of it for $5. New motor runs much quieter than the old one. Thanks for your help.

Total cost on this was about $107 CAP and fan motor. Figured doing this myself saved me few hundred dollars, maybe several thousand if they would have told me my compressor was bad.

New motor box from Grainger.

 
 

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