DIY Home Improvement, Remodeling & Repair Forum > Appliances > General Appliance Discussion > furnace buzzing/humming?




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Old 06-01-2009, 11:47 PM  
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.



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Old 06-02-2009, 09:46 AM  
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.









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Old 06-02-2009, 03:40 PM  
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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.

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Old 06-03-2009, 01:00 PM  
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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

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Old 06-06-2009, 10:50 PM  
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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.



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