During the winter time when I have my heat on, my outdoor air conditioner unit randomly makes this awful-sounding squealing/screeching sound. It lasts for about 15-30 seconds at a time, stops, and then occurs randomly again.

A Google search has revealed other people complaining about a humming noise, but this is anything but a hum.

It doesn't happen when I simply have the cool air on. It's only when I am using heat.

  • Is your system electrical? Commented Jan 4, 2012 at 16:34
  • It runs off electricity if that's what you mean. Commented Jan 4, 2012 at 16:39
  • I mean, is its heating source electrically based, as opposed to Gas or Oil (or Uranium 234)... Commented Jan 4, 2012 at 17:22

1 Answer 1


If your heating system is purely electrical (see comments), then your outside unit is not an Air Conditioner, but a Heat Pump, who's job is to take heat from outside (ha ha for you New Englanders and Mid Atlantic types) and bring it inside.

So your system is squealing because it's running as its supposed to, only it's cold outside, and the parts need lubrication.

Have your system checked/maintained by a qualified Heat Pump technician.

  • It actually does sound like it's in need of lubricant. Sounds like metal against metal now that I think about it. What kind of lubricant would you be able to recommend or at least give me a name or two to send me on my way to Google. Thanks Commented Jan 4, 2012 at 19:58

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