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  1. #1
    Join Date
    Jul 2008
    Posts
    35

    Fan or compressor making oscillating humming noise

    We have a 4 ton York heat pump outside our bedroom. Since it has started warming up, the AC has been running and there is some noise coming into the house. The noise is sort of a humming, but the pitch oscillates back and forth every second or two, and then sometimes stays constant for a little bit, then starts oscillating again, sort of like the vibration is coming into phase and then drifting out of phase.

    I don't hear the noise when it's just the air handler running. The AC has always made noise but I don't remember it being like this last year, although it's hard to say. Can you give me any ideas what might be causing this?

    I am a light sleeper and normally I like the constant drone of an AC to help me stay asleep. However this variable noise is making it hard for me to fall asleep. My wife doesn't hear it but I do.

    I am not looking for DIY info, just some ideas so I can tell the tech what to look for. Odds are the tech might not hear the noise like I do, it is subtle but annoying.

  2. #2
    Join Date
    Apr 2010
    Location
    Southeast
    Posts
    40
    Too many parts it could be to say without looking at it. Or in your case hearing it.

  3. #3
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,793
    Kind of hard for us to say what could be causing it. Since we can't hear it either.
    A tech on site would have a much better chance of hearing it, then us just guessing. Without checking anything else.

    Give him the same description you gave us.
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  4. #4
    Join Date
    May 2010
    Location
    Florida
    Posts
    15
    Just a possibilty but sometimes when the service cover is not tight it will do that.

  5. #5
    Did you ever get an answer to your oscillating fan noise issue? Mine is doing the same thing.

  6. #6
    Join Date
    Nov 2008
    Location
    SW Florida
    Posts
    23
    I just snugged up every screw on the outside of the unit. They are sheet metal screws, don't strip the metal out, that took care of it.

  7. #7
    Join Date
    Jul 2011
    Posts
    354

    Thumbs up

    Quote Originally Posted by Gulfside View Post
    I just snugged up every screw on the outside of the unit. They are sheet metal screws, don't strip the metal out, that took care of it.
    that's why you make the big $$$$$$$$$$$$$

  8. #8
    Join Date
    Jul 2008
    Posts
    35
    Quote Originally Posted by aliceme View Post
    Did you ever get an answer to your oscillating fan noise issue? Mine is doing the same thing.
    Not really, I think tightening the screws helped some but the noise is still mostly there.

  9. #9
    Just fyi...I took off the cover for the intake vent and lined it with weatherproofing strip (the kind used around a door). Noise is gone.

  10. #10
    Join Date
    Jul 2008
    Posts
    35
    Quote Originally Posted by aliceme View Post
    Just fyi...I took off the cover for the intake vent and lined it with weatherproofing strip (the kind used around a door). Noise is gone.
    What part do you mean by "intake vent"? My compressor pulls air in over all the coils on the 4 sides and vents it out through the fan in the top. Maybe I need to put some weather stripping where the fan panel meets the box (e.g. the four corners of the top of the box)?

  11. #11
    Sorry for not being clear. I mean the vent in the bedroom where I sleep, not a vent on the actual unit. I took off the small (6x10?) vent that pulls air out of the room when the AC/ fan is running, put weather stripping on it, and put it back on. No more noise. It was an inconsistent whirring sound, so I wasn't expecting this to work, but it did. Good luck!

  12. #12
    Join Date
    Nov 2010
    Location
    Central Florida
    Posts
    556
    I've got the exact same droning hum problem, but haven't been able to figure it out yet either.

  13. #13
    Join Date
    Jul 2002
    Location
    Yuma, AZ
    Posts
    2,361
    Each motor and the compressor may generate a regular sound pattern with different frequecies. These sounds interfer with one another resulting in the increasing loudness and decreasing loudness pattern that you are experiencing.

    The physics is explained at http://www.physicsclassroom.com/Class/waves/u10l3c.cfm

    The principle of superposition is sometimes stated as follows:
    When two waves interfere, the resulting displacement of the medium at any location is the algebraic sum of the displacements of the individual waves at that same location.


    The solution: Isolation of one of the motors or the compressor (often with rubber) may help if one of the sound sources is driving something else to produce a sound (like a loose panel). Pressing on various components with a rubber tipped stick may help locate the source of the sound. Because of moving parts and electrical dangers, this may be best done by a pro.
    "I have never let my schooling interfere with my education."
    Mark Twain
    More at: http://www.quotationspage.com/subjects/education/

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