DIYbanter - View Single Post - Air Conditioner makes Loud Hum when starts then goes away

wrote:

On 26 Jul 2005 21:12:00 -0700, "J-Man" wrote:

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

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.

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