Fan motor on roof air conditioner

[Jerry Grass]

My 1979 motor home has a duo therm standard line roof a/c. Been having the problem that sometimes, when I turn it on, the fan motor just hums. Then sometimes when I turn it on, it comes on & blows cold air. I thought it was a bad capacitor so I had all 3 caps checked, 2 of them checked good, one of them was bad. So I replaced the bad one which they said was the start capacitor. I turned the unit on 4 different times during a 3 hour span & it came on every time. The next day, I turned it on & the fan motor just hummed again, like before I replaced the capacitor. When I spin the fan with my hand, the motor comes on.

Seems like the motor is stopping at a bad spot. I'm wondering if I should replace the fan motor or if the capacitor I got is not strong enough. The one I got is a 72-88 uf   250/220V

Should I replace the fan motor?

Jerry

[Lakota Wolf]

Did you go as far as to slide the Armature out of the windings to check for a bad spot? If the a/c unit sat for a long time, it could/would have accumilated a corrosion spot. I came across a similar problem on a furnace motor. It had a slight rust spot on the bottom side of the motor,(motor sits horizontal). I slide the armature out of the windings, and used a lil fine steel wool and cleaned up the bad spot and the small spot on the armature and re-installed,, making sure the *brushes were clean, and it seemed to have done the trick. This is just a suggestion, hope it helps a little.(I did spritz a little w/d 40 in there to rid any condensation.).

[Jerry Grass]

I did use it some this summer. Sometimes it would come right on but every now & then, I would have to spin the fan by hand. I did notice one time it ran for several hours then stopped blowing. The compressor kept running but then stopped because no air was blowing.

I don't know how to get that motor out of there but I'll figure it out. Has a Styrofoam box around the squirrel cage part of it & hopefully I can take that apart without busting it up.

[Lakota Wolf]

Good luck,, let us all know how it goes... Like I stated, I was just suggesting the armature having a rusty spot.

[Jerry Grass]

It's been too cold here for the compressor to come on but over the weekend, I turned the fan on several times & the fan came right on without a problem. I don't get it. If my fan motor is bad, why does it start every time & sometimes just hums even with a new start capacitor? I must have turned it on at least 10 times over 2 days & it came on every time.

[Ashley Young]

We had the same issue on our 1980 Brave.  Camping World said it was a bad start capacitor.  We replaced it, it ran better for a few days, and then the motor burnt up.  From what we found, I ended up purchasing a new unit online because we got tired of piecing it together every time we went camping.

[Jerry Grass]

Man, I would love to have the unit replaced but I just can't afford it. If I can get a fan motor for about $150, I can swing that. I dread having to take out the old one & put the new one in. I just know, with my luck, it's going to end up being a stressful job. I always read how easy a job is but when I do it, I find a bunch of other problems to deal with. At 62 years old & 3 back surgeries, it's tough sitting on that roof for any length of time.

[Curtis Parrish]

I have a Coleman on my trailer and I just switched it. Before I turned it on I checked the fan motor and there is a SMALL tube for oiling on each end. Mine was a little slow coming on also but after a few drops of (electric motor oil) it comes on and blows great so far. You might want to try giving a few drops of oil first before you spend the money for a new motor..Good Luck. Hurry Up Spring!!.

[Jerry Grass]

Thanks, Curtis. I'll have to get the styrafoam off the box & then take the box apart to get to that side of the motor to see if it's got a place to put in oil. The part of the motor with the squirrel cage is inside the box. The side of the motor that's exposed doesn't have any place to oil it.

I've been waiting for decent weather on a week end to get back up there & work on it but for the last 2 weeks, every time I turn the fan on, the motor comes on.