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dptadf · 07-07-2015, 01:51 PM

Need help diagnosing our AC unit. The fan motor on our Coleman Mac 1500 roof ac unit intermittentaly stops running. The compressor continues to run. I have changed the capacitors and the control unit inside the air return. All wiring looks good. Checked 12volt supply from stat it remains good even when fan motor shuts down. Any suggestions what to do next?

**Lt Dan** · 07-07-2015, 02:21 PM

Quote:

Originally Posted by dptadf

Need help diagnosing our AC unit. The fan motor on our Coleman Mac 1500 roof ac unit intermittentaly stops running. The compressor continues to run. I have changed the capacitors and the control unit inside the air return. All wiring looks good. Checked 12volt supply from stat it remains good even when fan motor shuts down. Any suggestions what to do next?

Sounds like it could either be an open winding in the blower motor, or a defective fan relay. The blower runs on 120v AC, not on 12v. The 12v from the tstat is for control only and should activate a fan relay somewhere. The relay may be incorporated into the control board that you have already replaced.

Jupiter · 07-08-2015, 08:48 PM

Lt. Dan gave you sound advice. Since it is an intermittent problem, my first two culprits would be 1) evaporator fan motor tripping on thermal overload, or 2) bad fan relay (12v/120v). If it was a low or high pressure trip the compressor would also shut down.

cheers,
Joopy

Ggrvusa · 07-08-2015, 10:22 PM

Had this problem 2x. Just change out the fan motor. Research the part # and buy a new motor. For my Mach 3 it cost about $150. Not that difficult to do.

Ggrvusa · 07-08-2015, 10:25 PM

Let me be more specific. My motor was sticking and hard to turn. If I accessed the hamster cage from inside the coach and gave it a few spins I could get it to work.

stink · 07-09-2015, 01:59 AM

do you have a coleman mach_ dual zone thermostat ? do you have flourecsent lights? If so on both you might have a ballast problem on one or more flourecsent lights. The defective ballasts will impart an rf signal into the 12v electrical and mess up the thermostats functions turning on or off items on its own. Mine would turn on the ac fan when you turned on the flourescent light above the kitchen or turn off the heater or anything else that you didnt choose

bobder41 · 07-09-2015, 05:42 AM

Replace the fan motor, the bearings are sticking causing it to overheat and stop

ahicks · 07-09-2015, 06:05 AM

Thinking thermal overload here too. Being cheap by nature, and having more time than money (retired), I'd be tempted to get a drop or 2 of oil on those bearings if the motor seems stiff, especially if it's spent a lot of it's time sitting unused?

Worst case, you're going to have to pull the motor anyway to replace it. If access to the bearings make it difficult or impossible to oil, why not pull the motor, put a couple drops of motor oil (whatever weight oil you have handy) on each end of the motor where the shaft exits, and try it? This isn't just a patch. Many motors will go for years once this is has been done. I've had success after success with the move. If you're doing your own work it's worth a try. If you're paying somebody, maybe not so much....

lavamanz · 07-09-2015, 12:25 PM

My fan would hum when the unit came on so I tried to oil my 15 year old Coleman Mach fan motor shaft & it lasted a month maybe. The shaft wasn't turning freely at all. I then replaced the fan motor & start capacitor & I was back in business.