Outside A/C fans runs all the time....very very slowly

CaBrit58July 3, 2011

Hi Guys,

Got a strange problem with the outside (American Standard) A/C unit. The fan was turning very very slowly all the time and humings. When I turned on the A/C the fans spins up but only to about half speed, and after about 5 minutes the whole unit makes a very loud buzzing sound.

So I replaced the main relay/contactor as the old one appeared to be sticking, and now the fan now hums as if it's trying to turn. It also still never gets up to full speed when the A/C come on. I replaced the motor 3 years ago along with the motor capacitor so I suppose one of them could have gone bad again, any suggestions?

Also, I am confused as to why the fan be trying to turn when the contactor is not energized.

Thanks for any help.


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Ok...did some more digging and I now know why the fan was trying to turn, hat case had become live and so it was acting as a neutral. I have never seen this before, is this common? All three wires have a resistance of 40ohms to the case, so what could cause that problem.



    Bookmark   July 5, 2011 at 11:55PM
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"now the fan now hums as if it's trying to turn"

Classic sign of a failed start capacitor.

It may have failed and energized the case of the unit.

    Bookmark   July 6, 2011 at 11:17AM
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