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motc777's avatar
motc777
Explorer
Jul 22, 2016

Massive Heat Wave, AC not working. - HELP

I have a Duo Therm roof AC unit. Yesterday morning it was blowing cold air, but sounded like the fan was laboring. Ultimately, fan stopped working altogether. Even with AC off and just switching fan to on, not working.

I tested the Start capacitor and run capacitor and they were both bad. At the same time I checked the fan and I could spin it freely so not thinking that the fan motor is burned out.

Got two new capacitors, and the compressor fires up, but still no fan starting up. I have double checked the capacitor and it is getting enough power and checks good. What could be the issue?

I did make sure from the thermostat that there was power getting to the fan contact. Any help is appreciated. It's 100 plus degrees and I am dying.

46 Replies

  • Update to what is going on:

    Bought a fan motor, and little did I know, it was an entire kit complete with a capacitor. What's funny is that I went to this same RV place earlier in the day, and they said they didn't have my model's capacitor. If I would have known it came in the fan motor kit, I would have just gotten that.

    So I setout to replace the fan motor on my Dometic. I think Satan himself must have designed this contraption! I started to take the squirrel cage off and I got to looking at it, and I didn't see any screws, bolts, nuts or anything. Then I looked and the cage that fits over the inner fan had these little metal tabs that you have to bend and the pop the whole thing off. It wasn't easy and took me over two hours to figure all of that out.

    Once I got it off, I saw a major problem. The threaded studs that are on the opposing side of the squirrel cage where the actual fan motor bolts onto, all three of them had rusted and broken off when taking the nuts off. At this point, I started to seriously consider throwing in the towel and just getting a brand new unit. But then I considered all the time I had spent to this point, and I kept thinking, "what am I going to do about those broken studs?"

    And then it hit me: JB's Steel Stick. I've used this on a transmission's dipstick tube that had a hole in it and it sealed that up good enough and hardened like steel, why not use it to mount this motor?

    By this time, sun was almost down, I was drenched in sweat so I have called it a night. I did however work on the rest of the job, like pulling the fan motor wires through the protective sleeve and putting them into the little connector that it fits into in the ceiling and getting everything else ready. Supposed to be 100 plus in Texas tomorrow. Oy vey!

    Edit: I forgot to mention that when taking the old motor off, I saw one of the wires to the motor had literally burned all the way through and was just hanging on by the plastic shroud around the wire. I thought of splicing it, but after all that work, I figured better to replace it.
  • smkettner wrote:
    I thought the start capacitors were primarily for the compressor.
    The blower fan motor should just run or get a new one.


    There you go thinking again:B Start Capacitors are required for both the FAN MOTOR and the COMPRESSOR. Doug
  • I thought the start capacitors were primarily for the compressor.
    The blower fan motor should just run or get a new one.
  • I had a fan motor that would spin freely but wouldn't run (at least not for long). Fixed it by replacing motor and capacitor. Interestingly it would work at a different motor speed, so that may be worth a try if your motor supports multiple speeds.
  • Hornnumb2 wrote:
    If you have power going to fan motor, fan is just burnt up.


    and that is evident by the fan side of the capacitor checking good? So just because it spins freely doesn't mean that it's not burnt up?

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