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Coleman roof AC motor

June 18, 2013, 12:10:24 pm

I discovered the fan motor in my Coleman rooftop air conditioner changes speed sporadically even though the bearings are good and it spins freely. I presume the motor needs to be replaced? I changed the capacitor with a known working capacitor from the other identical air conditioner and that didn't solve the problem. I didn't see any obvious damage to the unit when I opened it up other than mud dauber nests, which I removed. There were thunderstorms in the area and some power outages at the time it happened so maybe the voltage went even lower than it already is here in this campground and the motor got hot? I'm just speculating with no supporting evidence though. Where can I find a replacement motor? I'm presently in the Dallas TX area. I read on this forum that the only affordable source of motors is to find used ones from old discarded units... Anybody on here have an old one that works that they'll sell to me? ...I sent an e-mail to Fasco asking them where to find a motor but they haven't replied yet.

Fasco
No: 7124-1897
CPN: 6799-311
Type: U24B1
1/4 HP
3.1 Amp


Scott
(615) 482-7650

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Re: Coleman roof AC motor

Reply #1 – June 18, 2013, 01:57:13 pm

Scott,

My front roof A/C (Dometic/Duotherm; original A/C) does the same thing -- for about the first 10 minutes - it will surge, then slow down for a few minutes, then surge for a min., etc.. However, then it smooths out and is fine for the rest of the day. I have learned to live with it, as there is no bearing noise and fan turns freely.

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Re: Coleman roof AC motor

Reply #2 – June 18, 2013, 02:52:36 pm

It does still run, and I notice that it runs better on the medium speed than on the high speed. I ran it a while yesterday on medium speed. I was really hoping it was the capacitor. I don't know if a 20+ year old air conditioner is worth buying an expensive new fan motor for? I'm guessing it's gonna be an expensive motor if I buy it new? Maybe I can convert it to a more affordable motor? The rest of the unit still works and appears to be in good condition except for corrosion and some minor issues that don't affect its life span. I get the feeling it's not designed for full timing though. I hardly ever run both air conditioners, and the rear unit is in a more versatile location so I use it more. The front unit is the one with the bad fan motor. I still haven't heard from Fasco, the motor manufacturer. I guess they're real big on customer service?

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Re: Coleman roof AC motor

Reply #3 – June 18, 2013, 05:15:10 pm

Scott, At some point the mfg's of these units deleted an oil cup on the motor shaft.  The older ones can be lubricated.  The shroud has to come off, then you can see the oil cups.  You may have to remove the inner cover to get at one end of the motor to oil it.  On my 85 I had similar symptoms and this cured it. While you are at it clean up the coils and renew the foam gasket under the shroud. Depending on where you are check with an RV repair shop, they may let you have the motor out of a unit that has a failed compressor if that is what you need.
Worth a try.
Gary B

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Re: Coleman roof AC motor

Reply #4 – June 18, 2013, 06:14:55 pm

A unit that old is not worth repairing, surprising that it has lasted that long.  Could be the fan switch or just a loose connection to the switch.  If you just like fixing things then work on it.  I agree with what Gary said about the foam gasket that keeps the air circulating properly, that is usually the first thing to go, then the gasket it sits on to keep rain out.  A new unit will be quieter, as the old piston type compressors make more noise to begin with, then get louder with age.  The new units have a rotary type compressor. 

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Re: Coleman roof AC motor

Reply #5 – June 18, 2013, 06:30:34 pm

I doubt it's the switch because it slows down on medium speed, but not as bad as when it's on high speed. Maybe I'll call some RV shops and ask if they've got a used fan motor or a junk unit that still has a working fan motor in it. I'm trying to avoid putting a new motor in an old unit if the motor is expensive, which I suspect it is because I can't even find one on the internet. It would be a shame to throw the unit away with the compressor and everything else still operating perfectly. That just kinda rubs me the wrong way. Everything I own is old but it all works properly. This includes my U300.

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Re: Coleman roof AC motor

Reply #6 – June 18, 2013, 07:07:22 pm

You don't have to throw the old units away.  I sold mine rather quickly on Craigslist.  $50 for the old one and $150 for the newer one.  Ditto for a 14 yr old working Norcold refrig.  I don't like throwing things away either.  Maybe you can sell them before removing them.  I have found that Craigslist works with a good honest description and good photos.  I suspect newspapers hate Craigslist as it's free and your ad can have color pictures and a map of your location.  Run a wanted ad for the motor, someone might answer.  When you replace the old unit, there will probably be some black dirt on the ceiling that the new unit will not cover, but that's another problem.

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Re: Coleman roof AC motor

Reply #7 – June 18, 2013, 09:11:08 pm

Actually, I just noticed a motor on eBay but it's a 1/2 horsepower motor and draws more amperage, but it's the same RPM. I don't know if there's a fuse in the air conditioner that will blow if the motor draws too much amperage or if the bigger motor would work okay? Maybe I'll give that some thought and look the unit over for any clues as to whether the bigger motor would work. It's apparently a new motor and it's reasonably priced. There's nothing else wrong with the unit. Even the condenser is clean and the fins are mostly straight. It may have low hours despite its age, like the coach itself. I dunno, but the unit definitely is worth putting a reasonably priced motor in. A new rooftop air conditioner would be expensive. I like having two air conditioners, even though I hardly ever use them both at the same time. It's not an emergency so I can take my time and find a reasonably priced fan motor for it... Fasco never did return my email from this morning. Tomorrow I'll attempt to call their sales representative.

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Re: Coleman roof AC motor

Reply #8 – June 19, 2013, 09:41:38 am

Check your circuit breaker connection, the wire nut connection at the AC switch and  wire connection at thermostatic, I have found road vibration will loosen wire connections. 
Next lube motor bearings, this is a project. Obtain a Electric Motor oiler at a hardware store, the one that's got a plastic tube about 12" long.  The rear bearings you get at by removing roof cover, the front, remove ceiling cover and up to motor shaft.  Apply a small amount of oil on shaft by bearing, it will wick in, repeat several times with no power.  Wait an hour an run. I don't think you need a new motor.

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Re: Coleman roof AC motor

Reply #9 – June 19, 2013, 11:44:23 am

I took off the ceiling cover inside the coach and noticed on the wiring diagram that it's probably a Coleman model 6799 which apparently has an exhaust motor in addition to the fan motor. I didn't see any other motor while I was looking at it yesterday. I need to take the unit apart further and find this second fan motor if it's there so I can check it out. According to the wiring diagram the exhaust motor doesn't have a capacitor. I wonder if this exhaust motor runs only when the unit is in fan mode? The wiring diagram doesn't show any fuses but it does say to use a time delay 20 amp fuse, which I presume means on the incoming power line to the unit. This unit has an electric heater, which was optional according to the wiring diagram.

I have a "Zoom Spout Oiler" in my storage unit but I don't feel like digging through piles of stuff to find it so I'll buy another one at the hardware store. It's turbine oil and that's what I've always used for electric motors. The fan motor does have oil holes with a sticker that says to oil it every 6 months with SAE 20. It doesn't say to use only 2 to 6 drops of oil, which most of those stickers say because people always over oil them.

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