furnace buzzing/humming?

Discussion in 'General Appliance Discussion' started by Christian, May 27, 2009.

  1. May 27, 2009 #1

    Christian

    Christian

    Christian

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    Hello all,

    I recently noticed my furnace making a buzzing/humming noise (similar to a 60 Hz noise hum...) all the time.

    It does this even when off / not running. My fiancee says it's always done that, but I've never noticed it. It's loud enough that I can hear it upstairs (main floor) through the vents when the house is quiet.

    Anyone know if it's normal and/or what it could be?

    Thanks!

    Christian
     
  2. May 27, 2009 #2

    kok328

    kok328

    kok328

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    It could be a bad transformer or a contactor stuck closed.
     
  3. May 27, 2009 #3

    Christian

    Christian

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    Any idea how to tell which?

    Something I could fix myself?
     
  4. May 27, 2009 #4

    kok328

    kok328

    kok328

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    You have to inspect the components I referred you to.
    Once you ID the bad part and get it in stock, the replacement is only a few minutes of work.
     
  5. May 27, 2009 #5

    Christian

    Christian

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    So when looking at the components...how would I tell if it's bad or good??

    I'm sure it varies between models, but can anyone help me to identify either of these components also?

    Thanks.
     
  6. May 27, 2009 #6

    kok328

    kok328

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    If bad/going out; the transformer will be warm/hot and buzzing. If the contactor is bad; the contacts will be closed even though there is no power to the coil. Start by removing the panels from the unit and turn the power on (you might have to hold down the safety switch). Listen and/or feel for the buzzing noise and post back what you found and what it looks like.
     
  7. May 28, 2009 #7

    Christian

    Christian

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    I will pop the panel off and look in there tonight and let you know what I find.

    Thanks for all the help!!
     
  8. May 29, 2009 #8

    Christian

    Christian

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    OK I took off the panel and listened/felt for the hum...it was very hard to pinpoint.

    Here is a picture of what I'm working with:
    http://i668.photobucket.com/albums/vv45/darga19/0529090615.jpg

    If I touch anywhere on that silver "box" (that the circuit board is mounted to) or the circuit board, I can feel the hum. Also on either of the 2 other components mounted on the "box." It doesn't really stand out on one component more than another...and unfortunately I'm not sure what to look for.

    Hopefully the picture could help you tell me what to look for / inspect?

    Thanks!
     
  9. May 29, 2009 #9

    kok328

    kok328

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    Sorry, I can't see clear enough to tell what components are what.
    Can you post a pic w/more light in the cabinet?
     
  10. Jun 1, 2009 #10

    Christian

    Christian

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    I'll try to take some better / lighter pictures tonight and post them.
     
  11. Jun 2, 2009 #11

    Nestor_Kelebay

    Nestor_Kelebay

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    Christian:

    What you need to do is invest anything from $3 to $15 in a tool called a "Mechanic's Stethoscope".

    A mechanic's stethoscope is similar to a doctor's stethoscope, but it works in a different way. Because sound is no more than rapid variations of air pressure caused by physical movement of objects, a mechanical stethoscope has a metal "probe" which you touch to any part of a machine that you suspect of causing a noise. When you touch the probe to the part that's vibrating to cause the noise, the probe will also vibrate just as the part causing the noise will. The vibration of the probe causes a diaphragm in the stethoscope to vibrate, causing you to hear the same noise, but much louder, in the earphones of the stethoscope. Thus, you locate the source of the noise by touching the probe to the place on the machine where you hear the noise the loudest through the stethoscope.

    A mechanic's stethoscope will typically cost $15 for one made in the Good Ole USA to $3 to $6 for the same thing made in the Good Ole People's Republic. I've been fixing appliances for over 20 years, and having a mechanic's stethoscope to pinpoint the source of a noise is a "must have" tool so far as I'm concerned.

    I expect that if you were to touch the probe to the transformer in the top left corner of your your "silver box", you'd find that it's the source of the noise. Look for any screws holding that transformer down, and see if they're loose. If there are not screws, jam a toothpick under it to prevent it from rattling against that box metal.

    This place sells both the KD Tools and Lisle mechanic's stethoscope, both of which sell for about $15:
    http://www.thetoolwarehouse.net/c-259-stethescopes-noise-finders.aspx
    KD and Lisle are automotive tool makers that have been around since I was a kid.

    This place sells a similar thing, but probably made offshore for $2.25:
    http://www.dpciwholesale.com/cart.php?target=product&product_id=865&category_id=76&pabPageID=9

    and, Harbour Freight sells that same $2.25 stethoscope for $6:
    http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=41966

    I expect they'd all work equally well. Every DIY'er should have a mechanic's stethoscope to pinpoint the source of a noise. Without one, it's like trying to detect the source of a smell.
     
    Last edited: Jun 2, 2009
  12. Jun 2, 2009 #12

    Christian

    Christian

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    thanks for the info.

    I've used stethoscopes before...I'm actually a noise and vibration engineer...which makes it even more embarrassing that I couldn't pinpoint the noise lol. Now a clicking valve or timing chain whine I could tell ya something about lol.

    I will look at that and try the "toothpick jam" tonight.

    In the meantime...I tried to take some better / closer pictures of the components. Hopefully these will help.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  13. Jun 2, 2009 #13

    kok328

    kok328

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    Pic #2 (Tyco Transformer) is what I believe to be the source of the buzzing sound. I'm not saying to blindly replace it but, it's kinda hard to bypass without knocking out the whole system in which case it won't tell us anything. I think there about $25 bucks to replace just make sure it's of the same specs.
     
  14. Jun 3, 2009 #14

    Christian

    Christian

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    I actually tried the 'toothpick' thing that was suggested earlier...and it seems to work.

    There are 2 bent "hooks" using a type of springback fit to hold it in place against the silver "box", and it was rattling against it.

    I wedged a toothpick behind it and the buzzing seems to have stopped. Hopefully it holds up.

    Thanks so much for all your help guys!

    Christian
     
  15. Jun 7, 2009 #15

    Nestor_Kelebay

    Nestor_Kelebay

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    It actually wasn't a "lucky guess".

    An iron core transformer ALSO just happens to be an electromagnet that changes it's polarity rapidly if you put AC current through it's windings. In fact, with 60 Hz AC current going through the windings, one end of the iron core of the transformer will go from a magnetic north pole to a magnetic south pole and then back to a magnetic north pole 60 times per second, and so if the transformer can move, even slightly, and is in the presence of something magnetic that it push/pulls on, the transformer will vibrate back and forth at 60 cycles per second.

    Jamming a toothpick behind the transformer simply prevented the transformer from moving. That, in turn, prevented it from creating sound waves in the air, and that in turn "made it quiet". If it were held down to that "box" with screws, then tightening the screws to fasten the transformer down more tightly woulda done the same thing. By preventing the transformer from moving, you prevent it from creating sound waves as a result of that movement.

    Now that you know why the transformer will "buzz" or "hum" under the right conditions, determining that the noise was most probably coming from the transformer was, quite honestly, a "no brainer" (to be perfectly truthful).

    I expected it was probably the transformer, but for $15, it's a good idea to have a mechanic's stethoscope in your tool collection. That tool will allow you to pinpoint the source of noises in appliances and all types of machinery, and will normally pay for itself by just letting you know where the problem is.
     
    Last edited: Jun 8, 2009

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