Furnace blower squeals like that guy from Deliverance

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mylo

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When I got my coach, the blower motor on the furnace was almost completely seized. I managed to free it manually, and squirt some wd40 where I imagine the bearings are. I didn't remove it at all. The furnace works great, but does squeal pretty damn loudly for the first 30 seconds or so, after a period of inactivity. Then it abruptly stops (around the time it lights), and is fine. It works without any noise, if used within a few hours. As soon as it sits for a day or so, the same loud squeal happens. It is very baffling that it stops so abruptly (doesn't fade out).

Does it sound like a serviceable item? Anybody every repack the bearings on that DC motor? I imagine its probably sealed up pretty good, and I should just look for a replacement.

Thanks.


Mylo
 
Mylo:


It would help to know the model furnace you have.



The fan motor is replaceable and easily found but you will have a challenge getting the fan off the motor shaft to get it out. Before you do that I would suggest checking the fan alignment as that is what was wrong with our Atwood Hydro Flame. As the fan speeds up it aligns around the center of mass and stops squealing.
 
Mylo,

I just had the same problem with my furnace. Most likely the bearings are shot. I was able to remove mine and replace it but the new one had a loud whine. Got a second replacement which is running now. Still has a whine but not nearly as loud as the first one so I think I'll just keep it.

If you remove yours be careful The fans usually have a set screw or clamp. I damaged my mounting board and a new one was very difficult to find. Mine is an Atwood 8535IV
 
Another possible source of the noise is the fan rotor itself has slipped on the motor shaft and moved to the point where it is just slightly contacting the housing between the fan rotor and the housing. I had this problem and managed to reposition the fan on the shaft to increase the clearance and the noise went away.
 
Chet18013 said:
Another possible source of the noise is the fan rotor itself has slipped on the motor shaft and moved to the point where it is just slightly contacting the housing between the fan rotor and the housing. I had this problem and managed to reposition the fan on the shaft to increase the clearance and the noise went away.

Had a similar problem with mine. Had already purchased a new motor only to find out after pulling it apart that the fan was slightly rubbing the housing.
 
Mine makes a sound like that, but like that guy from Deliverance, ouch..
I haven't ever bn a round one that didn't make some noise.
With the winter going like it is I need to figure if I can lub it.
 
Easier to replace the fan, but as has been said, it can be a bit tricky.  I have replaced the fans in both furnaces, second one a lot easier with lessons learned.  Replacing the furnace usually just necessary if the burner box gets burned out.
 
We had the same thing, the furnace would squeal for the first 30 seconds or so, then stop.  Ours was that the fan was out of alignment. 

I would keep it simple and start there, then move onto bearings and/or replacing the furnace if realigning it doesn't fix it.

Marsha~
 
Mylo,

What brand/model  furnace?

At least on the Atwood 8500 series furnaces the fan motors use non replaceable bearings ... bronze maybe?  While they are generally considered throw away motors, others have been able to re-oil the bearings. 

While the jury is still out, I have re-lubed 2 motors so far.  As a matter of fact I will be changing one of those out today as it is making some noise on start up like yours and possibly running a little slow.  The one (call it #2) I will be putting back in I consider a better test of this method as I did a better job of re-oiling.

When I took #2 out it was hard to turn using the squirrel cage fan ... could not turn by hand with the fan removed without using a wrench.  Once removed gave it a couple of shot of WD40 (I know, not a lube) just to loosen it up.  Then over at least a couple of weeks, with the motor sitting vertically in a hole punched in a paper cup, would add 2 or 3 drops of light machine oil (3 in one oil) to soak down the shaft.  Next time by, would turn motor over and lube the other end.  Did this sporadically for at least a week or two.

When done it turned freely by hand.  It is the one I will be putting back in today .... will try to give an initial update afterwards.  Real test is how long it lasts ... but beats $50 and up for a replacement motor so far.  The last swap was sometime last year ... should have a note somewhere but haven't looked yet.

I did take a motor to my favorite generator rebuild shop and he said nothing to replace the bearings with FWIW ... we use our RV year round at different times so do put some hours on the furnaces.  Currently in Mojave, CA for a while and it has been getting down to around freezing give or take at night.

So as I said, jury is still out here, but it is doable if you want to go that route.  Change out on the Atwood is from outside and not too bad.

Howard

 
Jim Dick said:
I just had the same problem with my furnace. Most likely the bearings are shot. I was able to remove mine and replace it but the new one had a loud whine. Got a second replacement which is running now. Still has a whine but not nearly as loud as the first one so I think I'll just keep it.

Hey Jim,

Wouldn't the world be a much better place without all the whiners? :) :)
 
Howard R said:
Mylo,

What brand/model  furnace?

It's a Hydro-Flame 8520-II 16k BTU output. Maybe I'll try the 3 in 1 oil trick... I'll also try sourcing a new one. I am sure this is OEM, 23 years old...

I know the squirrel cage is not perfectly balanced... But that doesn't explain the sudden disappearance of the squeal, like clockwork, about 30 seconds after the first call for heat after a day of inactivity. Weird.


Mylo

 
But that doesn't explain the sudden disappearance of the squeal, like clockwork, about 30 seconds after the first call for heat after a day of inactivity. Weird.

The squeal is caused by shaft vibrating in the bearings.  When it vibrates it tends to catch a bit, with energy that should be rotating the shaft going towards the vibration and squeal instead.

If the motor can get the shaft above the speed that's causing the vibration and squeal, the shaft resumes running true.

I'll bet you have a bit of old lube in the bearing's bronze sleeve that has solidified and is catching the shaft when it's cold.  As soon as it thins out a bit either from rotation or the heat from being next to the flamebox, the shaft turns freely.
 
I have gone the lube route, but it is a temp fix, and removing and replacing the motor can be a PITA.  I replaced both fans (2 furnaces) and sourced through PPL in TX and Lazy Days parts.  The motor runs about $100.  I also have the 8500 series. the last 2 digits I believe signifies the BTU.  8520 is 8500 series 20k btu.

Depending on age of furnace there may be a set screw or a spring clamp on the fan.

 
Sounds like the "banjo syndrome" to me.  Reminds me of the guy who went to the doctor and said he can't get the song Green Green Grass of Home out of his head.  Doctor said it sounds like the Tom Jone's syndrome.  Patient said he never heard of it.  Is it very common?  The doctor replied "It's Not Unusual".

Not know the type of blower I would suspect bearings.  Then rotation alignment.
 
Howard R said:
While the jury is still out, I have re-lubed 2 motors so far.  As a matter of fact I will be changing one of those out today as it is making some noise on start up like yours and possibly running a little slow.  The one (call it #2) I will be putting back in I consider a better test of this method as I did a better job of re-oiling.

Ok, got rained out the other day ... not much but enough.

Changed the motor out yesterday with the re-oiled one I had (#2).  Turned it on and shortly popped the 7 amp breaker on the furnace. It does turn freely and ran quiet ... just  not for long.  :(

So this morning I got the meters out and after some checking found it was drawing around 14-15 amps DC ... didn't leave it on too long so as not to pop the breaker or blow the fuse up-line (again).  Checked the front furnace motor and it was drawing about 4 - 5 amps ... so found a new one on line for $50 with shipping. 

Just for the heck of it hooked the one I removed to the chassis battery and it was only drawing 1 or 2 amps ... but keep in mind there was no load on it ... just motor with bare shafts. 

FWIW - If you do this job note you will need long 3/8" allen wrench ... 6 or 8 inch ... to reach the set screws on the shaft.  Note also that the flat on the short shaft of the motor is offset 90 degrees from the flat on the long shaft.  The short shaft is on the combustion side and rather hard to see through the small access slot.

Howard
 
Please share your source!  Different furnaces, different motors, but mine were more.  As I mentioned before, I have replaced both of mine.  One of those jobe usually better to replace than to attempt repair.  The repair just doesn't seem to last long enough in comparison to cost to effort to R&R the motor. 

 
After re-reading all these posts, it sounds like a serious OEM design flaw. Bronze bushings are old technology. If I can determine the horsepower and RPMs of the original, then maybe I can find a comparable DC motor with actual bearings that might even be more efficient and draw less amps at Grainger. Triple benefit of increased longevity, no squeal, and more power to boondock. If not I'll just have to get a replacement.


Mylo
 

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