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Posted: 12/30/2015 2:33:44 AM EDT
The fan on the outside unit (Trane TWX036D100A)  attempts to start, but squeals to a halt after about 1/2 second.  The squeal sounds like metal on metal rubbing.

I took the motor apart and found nothing visible in the motor or on the fan blades that would explain the squealing.

Windings looked fine also.

I cleaned and lubed the sleeve bearings but the problem remains.

This motor costs about $280 for a new one so I don't want to just replace it to see if that works.

I'm stuck because the mechanical squeal implies binding or rubbing but I can't find any evidence of that at all.

Could this be a bad cap?  This unit uses an oddball run cap that costs about $80 (no shit, I've looked all over) so I don't want to just try one for giggles.

If not a bad cap, what else should I try?

A new outdoor fan motor?

Don't want to throw money at this randomly replacing parts.

Link Posted: 12/30/2015 2:35:18 AM EDT
[Last Edit: 12/30/2015 2:35:53 AM EDT by hanau]
tried spinning the fan by hand?





Bearing feel smooth or rough?




What is the part number of the fan motor?




 
Link Posted: 12/30/2015 3:12:15 AM EDT
so a couple of things.  
I found a generic fan motor at grangers that matched up except depth.
it works, but is in a little deeper than the shroud.

2nd, most are dual caps and you can rewire and buy a single cap to replace the part that might be blown.

both should be cheaper than the 280 you mentioned for the correct motor.

I agree though, you should see how it spins up by hand.

there should also be a way to force the fan and compressor on in the outside case so you can test it wired up and figure out where the squeel is and if you help the fan by hand if it will continue to spin after it stops.
you also don't mention how old this is.
Link Posted: 12/30/2015 3:27:39 AM EDT
Mine went bad but it was just the bearing. Rigged it up to run a couple of days but just so happens I have a Grainger discount through my employer. I ordered a generic motor for about 60 bucks and it arrived the next afternoon with free shipping thanks to the discount. Just look at the motor specs and give it a go. The HVAC man did come out to check it before I looked at it. I was at work and the wife called to tell me it wasn't working. He wanted $400 to replace it but said I really should get an entire new unit. All this for a sixty dollar motor.
Link Posted: 12/30/2015 3:56:37 AM EDT
[Last Edit: 12/30/2015 4:00:02 AM EDT by AZBADBOY]
Buy closest match at Grainger and move on.

You can seriously be a hvac tech if all you know is replacing condenser fans, caps and contactors. Not much else falls outside of that realm and if it does they will try to sell you a whole new system regardless
Link Posted: 12/31/2015 3:36:17 AM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Andrewh:
so a couple of things.  
I found a generic fan motor at grangers that matched up except depth.
it works, but is in a little deeper than the shroud.

2nd, most are dual caps and you can rewire and buy a single cap to replace the part that might be blown.

both should be cheaper than the 280 you mentioned for the correct motor.

I agree though, you should see how it spins up by hand.

there should also be a way to force the fan and compressor on in the outside case so you can test it wired up and figure out where the squeel is and if you help the fan by hand if it will continue to spin after it stops.
you also don't mention how old this is.
View Quote


It's a unit from 2002 so kinda old.

For whatever reason, it's a two-speed fan and no generics are exact replacements. I guess I need to try running it on its own to figure it out.

It does spin freely by hand, and pushing/pulling on the fan doesn't cause any rubbing.

It's odd, though- a bad cap causes the motor to just sit and hum usually, and a loud squeal means a mechanical problem but there's no mechanical problem that I can find.



Link Posted: 12/31/2015 12:52:45 PM EDT
call up granger and see if they can find one.
Link Posted: 12/31/2015 12:55:53 PM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Andrewh:
call up granger and see if they can find one.
View Quote

Or just take it down there. I'm sure they will have a match.
Link Posted: 12/31/2015 12:57:31 PM EDT
bad bearings
Link Posted: 12/31/2015 1:01:07 PM EDT
Link Posted: 12/31/2015 1:11:12 PM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By coldair:
bad bearings
View Quote


+1

Replace fan or upgrade system.
Link Posted: 1/1/2016 8:29:27 PM EDT
An update: (and thanks for the replies, everyone)

Bad bearings it is but the bearings aren't binding.

The motor spins fine when spun by hand.

I bought a run cap and ran it on the bench and it jammed.

Turns out that the shaft is worn just enough for the rotor to snag on the stator when energized.  The wear is on one side of the output shaft; fan is probably out of balance.  Sintered bronze bearings FWIW.

Local HVAC place didn't have a replacement.  Didn't see anything suitable on Grainger's website but I'll give them a call.

It's a two-speed motor and I haven't found a good explanation for why it is.  The speeds are switched by the defrost control board (which also had issues, broken solder joints from vibration specifically)

My (very short term) fix was to put the rotor on a little wood jig I rigged so it could spin somewhat freely and to then take a belt grinder to it to reduce the OD enough that it isn't jamming.  If I had a lathe big enough and stock on hand I'd just make a new shaft (but the bearings are worn and not replaceable so it'd still be a short term fix)

So it's off to buy a new motor on Monday.  Here's hoping my fix lasts that long

TL;DR-worn bearings and shaft let the rotor jam against the stator. Cheesy fix in play temporarily.

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