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Old 04-06-2012, 10:27 AM   #1
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Air Conditioner fan motor help

i have a carrier heat pump. at the end of the summer, the fan slowed down and made a rumbling noise. i thought the problem was bearings or lubrication of bearings. checked play on shaft and there wasn't any that i could feel (we know there has to be or it won't turn). shaft turned free. disassembled motor and the bearings were lubricated. sense i had it appart, i added a little machine oil and put it back together. well, after if runs abt 15 minutes, the motor slows down. i shut it down at that point so i don't know if it would rumble or not.
have not changed the capicator but did a visual and it is not distorted.

electric motors are not one of my strong points. and suggestions?

oh, compressor and sealed system works fine.
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Old 04-06-2012, 11:06 AM   #2
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I would say there's a short in the windings and as motor
warms up the short limits the voltage in turn slowing down motor.
take it off and visit a local grainger if you have one nearby.
If possible get numbers off it and call first.
I'm lucky my grainger is 5 miles away.
They also have an online catalogue
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Old 04-06-2012, 01:02 PM   #3
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that is probably going to be the end results. i was hoping it wouldn't be a replacement.
i still have one other test to run and that is with a clip on amp meter. it will probably take me awhile to get back up there. might do that just before i pull it.
we have an appliance parts (inc) and a grainger's abt 30 miles away.

on one web site, someone posted that the motor was available for $300. that seems abt $200 too high to me. believe if that is the case and i can't adapt something, i will change the whole thing out with a low profile.

if i could find the short, i may be able to spray some of that high voltage spray on it. believe finding it would be like a needle in a hay stack.

thanks for ur help.
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Old 04-06-2012, 01:18 PM   #4
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Assuming its a brushless motor I believe my first post "pretty"
Accurate in my experience.
now with that said if there's no voltage drop at motor I firmly believe I'm correct.
I would double check for voltage loss first.
Ie fan motor controller issue,fan relay,circuit board issue.
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Old 04-07-2012, 02:08 PM   #5
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it is brushless (induction?) motor. we are on the road now. will dig into it when i get home.
after getting to this campground, i turned it on and got the noise on start and couldn't get it to go until i put it on high fan. my only alternative may be to go back into it.
the speed switches are mechanical. sealed system works fine. ie i don't think there are any controllers on that section..but will varify voltage out of the switch.
if i can get rotation again, i will put a clip on ammeter on it and see what it reads. if amps go up as it slows down, would expect that to be normal but wouldn't know what conclusion to draw from it. if the capacitor is bad, i don't know what to expect from that. i would guess that it is a run capacitor.

most likely, ur suggestion abt it being a short in the windings after heat up sounds like the most reasonable.
i have a reunion coming up so it will probably be abt a month before i can get back up there. the voltage check, i can do as soon as i get home. can do that from inside the camper.
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Old 06-08-2012, 09:23 PM   #6
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found a motor that was correct speed and hp at grainger for just under $200.



the replacement motor was shorter and larger diameter.



made a new base to elevate the motor to the proper height out of 2.5" OD square tubing.

installed the base with motor cradle and made measurements before cutting the shaft.

the replacement motor is a AO Smith 4UU30. figured the base and screws cost abt $25.

for anyone that finds they need to replace the fan motor in a carrier ac, this is much cheaper than the $380 that i heard the carrier motor cost. seems that those that still have the carrier parts are selling them by the troy oz.

motor is reversable which takes the worry out of cutting the shaft.
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