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Old 08-21-2008, 07:32 AM   #1
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I have a roof mounted a/c unit and all it does is hum. Any suggestions?

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Old 08-21-2008, 07:32 AM   #2
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I have a roof mounted a/c unit and all it does is hum. Any suggestions?

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Old 08-21-2008, 07:45 AM   #3
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momike if it sounds like the compressor is humming. I think your fan capasitor is no good if your a/c is a coleman. If it's a dometic see if you can turn the fan could be froze up. This will hape if not used too much.
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Old 08-21-2008, 07:52 AM   #4
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Do you know if the compressor is running or not? If the hum is the compressor running and the fan does enot run, you may have a bad start capacitor on the fan motor or a bad fan motor.

With the A/C off and preferrably with the A/C breaker in the OFF position, remove the outside cover from the unit. Now, see if the condenser fan motor will move easily. If it rotates easily, have some one turn on the A/C breaker and stand by the A/C thermostat. Spin the fan by hand and tell them to turn on the A/C unit.

BE VERY CAREFUL around the open and exposed fan.

If the unit then runs normally, you probably have a bad fan capacitor, which can be found at some hardwear stores and A/C supply houses.

Be sure and kill the power to the u nit and short the terminals on the capacitor to drain the charge and not shock yourself.

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Old 08-21-2008, 08:29 AM   #5
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> ... all it does is hum. </div></BLOCKQUOTE>

What's the name of the tune your A/C unit hums?

You don't say whether your unit is blowing any air. If there is no airflow, it's possibly a problem with the fan and/or motor that drives it.

I have a Coleman Mach III A/C unit and I don't use it very often. I had a problem once where my fan wasn't turning. I was able to reach the inside fan by removing the return air grille/filter in the ceiling and then removing the screws that hold the metal plate covering the main cold air duct. Once removed, I could see the fan. I reached in there (with the unit turned off, naturally) and tried to move the fan. It was real stiff (most likely from lack of use), but as I kept moving it, it turned easier and easier. Once it felt pretty loose, I tried starting the unit and the fan began working again. I put everything back together and it's worked OK ever since.
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