Repairing A/C window unit fan motor

[Mike Bates]

I couldnt find a newsgroup to put this in, so im putting it here.

I have an older window A/C unit, it has a 2 speed fan motor.

When I turn the unit on, the compressor starts, but the fan motor just
hums. The fan motor bearings are well lubricated, because the fan spins
very freely.

I put the fan on low speed, and give it a little push, and it takes off,
but accelerates very very slowly. it will run, but the motor will get
red hot and the fan will slow down to a hum again.

The motor will not run on high speed, it just hums loudly, and pushing
it wont start it. it will go in either direction I push it.


I tried replacing the motor start capacitor, and it didnt affect
anything. Im guessing the start coil is open or something.


New motors are very expensive, and this is an older model, and I cant
find the motor for it. I would like to be able to rewind this motor.

Im good with electronics, I might take a shot at rewinding this motor.

Any ideas?

 

[techforce]

Sounds like the Front Bushing on the Motor is seized.

 

[Wayne Tiffany]

Not if the blade spins freely.

WT

 

[Mike Bates]

couldnt be, because it spins very freely.

if i try to spin it while on high, it wont, cause the force from the
magnetics.

if its off, it moves very very freely, no rubbing, no seized berrings as
I know of.

 

[Rick]

Try posting this in alt.hvac, lots of helpful folks there. Also a fair number
of arrogant idiots. Be forewarned.

Rick

 

[Shell]

Check start capacitor 5uf-30uf
Good luck!
Shell

 

[Mike]

as i posted, I replaced it.

 

[gonzo]

I couldnt find a newsgroup to put this in, so im putting it here.

I have an older window A/C unit, it has a 2 speed fan motor.

When I turn the unit on, the compressor starts, but the fan motor just
hums. The fan motor bearings are well lubricated, because the fan spins
very freely.

I put the fan on low speed, and give it a little push, and it takes off,
but accelerates very very slowly. it will run, but the motor will get
red hot and the fan will slow down to a hum again.

The motor will not run on high speed, it just hums loudly, and pushing
it wont start it. it will go in either direction I push it.


I tried replacing the motor start capacitor, and it didnt affect
anything. Im guessing the start coil is open or something.


New motors are very expensive, and this is an older model, and I cant
find the motor for it. I would like to be able to rewind this motor.

Im good with electronics, I might take a shot at rewinding this motor.

Any ideas?

Have you checked continuity in the windings? Any smell of burnt windings>
Alas, rewinding this yourself may prove difficult. Motors use special
materials
for the insulation, and are usually dipped in varnish and baked at a high
temperature.
The materials used are not normally available to the DIY man......

 

[Sam Goldwasser]

Sounds like the Front Bushing on the Motor is seized.

Did you read the posting? He said it spins freely.

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[techforce]

Yes I can read.....quite well FYI.

I just did a Fan that had the bushing partly siezed enough where it was just
enough to prevent the electrical field from starting it going, but moving
it slightly by hand would get it going.

I suspect this happens when the Fan is operated for a LONG Time, and the
Heat of the Armature causes the Clearance problem.

 

[Bennett J. Price, Ph.D.]

take a look at www.grainger.com they might have a cheap replacement

 

[techforce]

Yes indeed. My Fan exhibited the same problem. It would also not be able to
start up when you went to high speed from off position either, just like he
said.

Might be Cheap Iron used as the armature, because when I struck mine with a
Hammer, it dented quite easily. I think this type of metal swells more
readily when heated than say Tempered Steel. Cheap Production line mentality
again.

 

[Mike]

ok, here is the scope.

the motor has 4 leads going in. 1 is ground, 1 is start 2 are run.


there is no run cap, i think its single phase, so its only got a start cap.

lightly pushing it doesnt start it.

What i meant was, when i take my finger with all of my force and spin it, it
will begin to accelerate.

it wont work in high.

the motor eventually accelerates to the low speed top. i think. if i put it
on high from there, it will slow down to none very quickly.

if i leave it on low, the fan will run for about 5 minuts and then start
gradually slowing down to a hum, because the motor is VERY HOT.

 

[Shell]

I encountered on same symptom before. a lot of ants they ate some paint in
core and cause short after unassembled.

ok, here is the scope.

the motor has 4 leads going in. 1 is ground, 1 is start 2 are run.


there is no run cap, i think its single phase, so its only got a start cap.

lightly pushing it doesnt start it.

What i meant was, when i take my finger with all of my force and spin it, it
will begin to accelerate.

it wont work in high.

the motor eventually accelerates to the low speed top. i think. if i put it
on high from there, it will slow down to none very quickly.

if i leave it on low, the fan will run for about 5 minuts and then start
gradually slowing down to a hum, because the motor is VERY HOT.

 

[Sam Goldwasser]

ok, here is the scope.

the motor has 4 leads going in. 1 is ground, 1 is start 2 are run.

Ground or Neutral? You don't have enough wires for a 2 speed fan as
described.

there is no run cap, i think its single phase, so its only got a start cap.

lightly pushing it doesnt start it.

What i meant was, when i take my finger with all of my force and spin it, it
will begin to accelerate.

it wont work in high.

the motor eventually accelerates to the low speed top. i think. if i put it
on high from there, it will slow down to none very quickly.

if i leave it on low, the fan will run for about 5 minuts and then start
gradually slowing down to a hum, because the motor is VERY HOT.

Do double check that it is not mechanical. We think this to be the case
but push and pull shaft from end-end and side-side and make sure it has
no evidence of binding. Assuming it turns freely even after the 5 minutes
(assumeing you can touch it!!), then it's likely a problem inside the motor.

If it is indeed a start cap, then if it is disconnected once it starts
spinning should make no difference. However, how do you know it's a
start cap? A two speed fan would probably not have a centrifugal switch
inside so the start cap would have to be disconnected some other way
once it gets up to speed. A fan motor may indeed have a run cap and no
start cap.

At this point, I rather expect it's a problem inside the motor and replacement
will be the only realistic option. You might be able to find used one at a
salvage yard, or at a motor rebuilding or appliance service place.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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| Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the Feedback Form at repairfaq.org. Thanks.