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Discussion Starter · #1 ·
Hi. My Lennox furnace makes a squeaking /whining noise every time when it is powering down and to a certain extent when powering on. I posted a video on youtube:


I replaced the filter and vacuumed around the inducer and blower fan and also lubricated the bearing of the inducer fan with WD40 without resolving the noise issue.

Does anyone know where this noise is coming from and what I could do about it?
 

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Can't tell from the video.
But Harbor Freight Tools sells a mechanics stethoscope for about $5.
Without getting it stuck in a moving part it will allow you to pinpoint where the noise is coming from.
 

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It sounds like the metal on the fan is howling.

There is a particular quirk on about 1% of those fans. You have to remove it and where you see the metal on the sides it is crimped and folded over on the edges. For some strange reason I have had to put silver foil on those seams to make them tighter.

Sounds very strange but one of my fellow Lennox techs found that out and showed me the solution. Very strange as it does not seem loose.

There may be other metal loose or the motor bearings are worn and getting tight but those fans have ball bearings and run a long time. Ball bearings can fail too.
 

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The inducer fan is in a plastic body and cannot howl. It also does a self calibration routine and runs thru a series of different speeds to calibrate the pressure switches when it starts.

That sound is from the blower fan.
 

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Discussion Starter · #6 ·
It sounds like the metal on the fan is howling.

There is a particular quirk on about 1% of those fans. You have to remove it and where you see the metal on the sides it is crimped and folded over on the edges. For some strange reason I have had to put silver foil on those seams to make them tighter.

Sounds very strange but one of my fellow Lennox techs found that out and showed me the solution. Very strange as it does not seem loose.

There may be other metal loose or the motor bearings are worn and getting tight but those fans have ball bearings and run a long time. Ball bearings can fail too.
Thank you for helping me with my other problem in a different thread.
Regarding the noise issue coming from the blower fan, could you please indicate on this picture where to exactly put the foil on (would aluminum foil work?)

 

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On the front of the fan/flat part that faces you when you first see it then it goes over to the sides and round curved part you see at the bottom of your pic. You will see it is creased and folded over.

Tape those seams and make sure the plate that is inside the fan above the wheel is tight. It has 2 screws going into it that exit the side of the fan.

Post a pic of the front of the fan and inside and maybe I can past some arrows with MS Paint and help better.
 

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Discussion Starter · #8 ·
On the front of the fan/flat part that faces you when you first see it then it goes over to the sides and round curved part you see at the bottom of your pic. You will see it is creased and folded over.

Tape those seams and make sure the plate that is inside the fan above the wheel is tight. It has 2 screws going into it that exit the side of the fan.

Post a pic of the front of the fan and inside and maybe I can past some arrows with MS Paint and help better.
Sorry for the delay. I removed the blower fan and taped around the curved parts using aluminum foil tape.

Before:



After:



I have also tightened the screws of the plate above the fan


Beside of this and vacuuming the fan, is there anything else I can do while the blower fan is removed from the casing?
 

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Discussion Starter · #10 ·
For some strange reason I have had to put silver foil on those seams to make them tighter.

Sounds very strange but one of my fellow Lennox techs found that out and showed me the solution. Very strange as it does not seem loose.
I don't know how and why, but taping these seams completely eliminated the noise! Thanks again for your help
 

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I don't know how and why, but taping these seams completely eliminated the noise! Thanks again for your help
Yeah it is very bizarre. All the more so because in my experience/IMO Lennox has the heaviest thickest metal in their fan bodies and VERY rarely howl or have vibration problems.

Unlike some other brands which are held together with #6 sheet metal screws and made from tinfoil.

Probably a small percentage of ECM motors have a harmonic resonance at a certain speed and unless those joints were solid not spot welded they are not perfectly tight and the metal resonates.

Like I said it is less than 1-2% of them that do that and there are LOTS of those ECM V drive fans out there.

Glad you got it fixed.:vs_cool:
 

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Resonance has been both rewarding and bedeviling for engineers for ages. Electrically it make possible radio and TV but when mechanical it can cause large tower and bridges to collapse. Much is know about how to avoid certain lengths of towers during construction to prevent resonant collapse. All of it was learned the hard way.

This is the first time I've heard of a SC fan housing having a resonance problem. It sound a lot like the noise a blower wheel makes when it's slipping on the motor shaft. Sleeve bearing also make that same noise.

Very interesting to hear about it.

I witnessed how resonance affects mechanical towers once while I worked in SoCal. There was a tall steel pole that had a sign on it at one time but it had been removed and the pole stood alone with no load on it. It oscillated detectably 24/7 for months and months before it was finally removed. It was pointed out to me by our job site forman. I suspect it would have eventually have collapsed but that was prevented by progress and it was taken down. I was told later by a sign contractor that there were certain combinations of support poles/sign sizes that are not safe.

Check out some of the info on the link below and you'll see what I'm talking about.

Tower Resonance
 
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Yeah I suspect because that fan has a ECM variable speed motor it can set up a harmonic resonance.

I watched a video about famous bridge collapses in the US and a lot was learned the tragic and hard way.

One of the more interesting sights I got to see first hand was thermal expansion of metal.

I was at a University steam plant as a student and my trainer said do you want to see a pipe expand?

He opened the blowdown line for the water column ( where the gauge glass for viewing the boiler water level is ) on a 3 story 2000 hp steam boiler with superheaters running 175 psi.

Steam ran through for a minute and you could actually watch the 1/2" black iron pipe expand about a inch as we made a mark on it to compare it to the pipe beside it.

He shut the valve and you can watch the pipe contract. Pretty cool ( no pun ) to actually watch expansion and contraction not just talk or learn about it.
 
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