Air Conditioner makes Loud Hum when starts then goes away

I am a new home owner and I am starting to understand why my Dad got frustrated all those years when something broke in the house. I have just bought a townhome here in Houston. The compressor units are mounted on the roof. When the AC starts, there is a loud humming noise (i assume it is the compressor starting up) for about 15 seconds and then it drowns out. It cools fine and works great other than the noise. My neighbor is complaining to me saying it creates to much noise. What causes this loud hum when it starts? I know that there is always going to be some kind of hum, when it starts, but this is out of the ordinary. Any suggestions or tips are appreciated. Thanks.
Joseph
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Some compressors are just a little bit noisier than others, even among specimens of the same model.
Or it could be vibration in the lines. It damps out as headpressure builds up. If so, something up there could be missing or broken.
It even could be a problem with the installation, and can still be fixed, but will probably require opening the system, and that requires a pro...
If it's an older townhome, maybe the neighbors got nowhere complaining to the previous owner, but now that you moved in... food for thought...
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-john
wide-open at throttle dot info
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Suggest let him pay to inspect and fix it, if its indeed broken........
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SVL






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In alt.home.repair on 26 Jul 2005 21:12:00 -0700 "J-Man"

I'm not sure what you mean. Drowns out what? AFAIK, "drowns out" must be followed by another noise. The first noise is louder than the second and drowns the second noise out so that the second noise can't be heard.
Maybe you mean it fades out?

Meirman -- If emailing, please let me know whether or not you are posting the same letter. Change domain to erols.com, if necessary.
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The First loud hum fades out to a low hum.
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It happened to me when the idiot A/C guy over charged the system. Get a pro to check it out. IF that is the case, eventually the compressor will die causing a much bigger repair bill. As far as I could tell the idiot did not compensate for ambient temperature when he filled the system during the last service call (it was a cold day).

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Thanks, I will have an AC guy check it out.
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One other thing to check is the wiring. Is the gauge heavy enough for the starting load? I used to work at a place where the actual wiring in the walls would hum when the AC started. You could hear it throughout the whole building. There was a repair guy there one day and I asked him about that. As soon as he heard it, he said the wiring is too small for the load. He checked, and it was too small. His method of explaining the hum was because the wires were in steel conduit and the load actually made the wires heat and vibrate in the pipe. The sound was eerie. They rewired it a few days later and I never heard that again.
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snipped-for-privacy@invalid.com wrote:

And if the wires are too small you have a safety issue.
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