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Noisy defrost cycle thumping

It has been explained to us that the thumping (sounds like a small tom-tom) is to be expected when the unit is defrosting. Now that we've hit the 30 degree mark this is happening every night.

The problem is the noise. Last night I was awoken at 4:30 and again at 5:45 (we have two units- not sure of the culprit). I can understand the need for the cycle, but I can't believe it was designed to be so noisy it would wake you up! The units are outside at ground level, free standing house; bedroom is on 2nd story, same wall as heat pumps.

Is this normal? or is there a fix?

Posted by JBraren on

  • JBraren Nov 17, 2007

    Thanks for the info- I think we're headed in the right direction, but just realized that I didn't include in my first post that this thumping goes on for 10 - 30 minutes or more at 1 -2 second beats.

    This is too rhythmic for falling ice ( there isn't any ice build up) and it can't be great for a switch to be slamming back and forth with this intensity for this long-

    Any other ideas?

  • Anonymous May 07, 2009

    i have had the same problem,i ut was defroster fan ...replaced it

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fixr1st

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  • 49 Answers

The heat pump works like this. Your outdoor units are now your evaporator, meaning that now they get cold, they will build a layer of ice and they will need to go thru a defrost cycle, either iniated by time or temp. When the cycle starts your system actualy switches back into cooling, turns off your outdoor fan, and brings on your heat strip. The noise you hear is either you reversing valve switching or the ice being melted, then being sucked back into the fan when your unit switches back into the heat mode.

Posted on Nov 17, 2007

  • fixr1st Nov 17, 2007

    It sounds like your system is switching in and out of defrost. If your system is new enough, only two things if the system is charged properly with freon. Defrost board or defrost sensor mounted on the condenser coil. Many newer boards have the sensor mounted to it, so it is all one item.

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