Dometic A/C fan start

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Apr 13, 2011 | 03:51 PM

golfgooroo

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Dometic A/C fan start

My A/C fan humms when power is applied to it. I've already replaced the run and starting capacitor. It also spins freely with no power applied. So my question is: "Is there a difference in spinning it by hand without power vs with power? From other forums it sounds like this has helped when the shaft/bearings rust over the winter on most units, but i don't understand how it differs whether the fan is turned on or not when making the shaft turn. Any input would be appreciated.

Apr 13, 2011 | 06:34 PM

BPofMD

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From: Millersville, MD

I would imagine that the HUM you hear is probably coming from the motor/ motor windings itself. And except for replacing the whole motor you won't be able to do anything about it. And prob cheaper to replace the whole fan assembly ! How old is it?

OOPS... didn't see that it was the air conditioner. Was thinking the fan in the skylight or bathroom exhaust. How old is the trailer? A/C same age?

Apr 13, 2011 | 07:16 PM

HrdDrv

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From: Baltimore

If it spins free without power applied, but hums, (no spin?) then the motor/wiring is at fault. Another question will be is amps at plug. 30 is the norm for ac. Is the ac charged to specs? (freon) There's also the panel box with the ac and mains breakers to check.
If you can power up the ac, and the fan powers up, the squirrell cage(fan) obtained a passenger. Hang in here, I'm hoping to see this resolved.

Apr 13, 2011 | 09:28 PM

daveshomeservice

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I think the difference between spinning w/power,or manually, is that little electric motor has no torque,to break free the corrosion. When you spin the fan by hand, you apply enough torque to break it free. I have to spin, and lubricate the a/c fan manually at the beginning of each year, or i have the same problem.

Dave

Apr 13, 2011 | 09:59 PM

HrdDrv

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From: Baltimore

An air duster (Can spray) would be in order for the wish list, as it would help with the vents, also. Nice call, and thanks for the info. Props to ya. I do believe the tech term is called "Stiction" It started with hard disk drives in computers not wanting to start up on thier own until they were 'helped'.

Apr 14, 2011 | 10:18 AM

rvpuller

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From: Home Base Nebraska

Quote:

Originally Posted by golfgooroo

If the bearings are worn the motor sometimes will still spin by hand but when power is applied the rotor will be pulled against the stator (windings) and make a very load humming noise. Give the motor a spin and apply power and see if it takes off, if it does then it's the start winding, capacitors or dry bearings, if it comes to a fast stop the bearings are worn and the motor needs to be replaced. Also I have never seen a start capacitor on a fractional blower motor just a run cap, if you replaced a start cap it was for the compressor not the fan motor.

Denny

Apr 19, 2011 | 03:41 PM

golfgooroo

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I guess I'm at a loss...I replaced the motor last year to get rid of a bad bearing that was loud even though the A/C would start up nicely. I'm testing the camper while plugged into a 30A plug, I've triple checked the wiring, replaced the capacitors, and it still humms. When I get home, i'll try to start it and give it a spin to see if that solves the problem. Only other thing I can think of would be if the wire colors have changed from the various models...When replacing the motor, I connected the yellow to yellow, red to red, and green to green, but I think it's a safe guess that this would be correct since the motor was a factory matched replacement. still a mystery...and yet summer is fast approaching!