Furnace fan motor making a lot of noise when starting

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Old 12-29-11, 10:37 AM
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Furnace fan motor making a lot of noise when starting

I have a Benjamin wood-electric furnace that is quite busy right now as the temperature is around -25C (about -13F). My furnace fan was making some strange noises when starting and then finally quit making an awful screeching sound. I opened the fan panel (after turning off the breaker for the fan, and the one for the electric furnace). I then loosened the fan-belt, and removed it, then removed the actual motor from the top of the fan assembly. I sat it on the cool concrete basement floor for a while and then heard a "click" sound. Everything being disconnected from the power I thought it could be the thermal protection, so turned the power on to the motor with the breaker and it started fine. I then lubricated it with some SAE20 oil as directed on the label and reinstalled it after making sure that I could freely spin both the wheel on the motor and the one on the fan.
When restarting it it still made the loud noise, I was wondering if anyone could point me in the right direction. I have recorded a short movie of me turning the breaker on for a short time and then back off to illustrate (audio) the problem.
Emerson 1/3HP furnace fan start-up noise - YouTube
The fan motor model is an Emerson Model SA55NXTE-4494, 1/3HP, 1725RPM
 

Last edited by Herring; 12-29-11 at 10:46 AM. Reason: Couldn't get the link to the video to display
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Old 12-30-11, 07:30 AM
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Hi Herring...based on your post, the motor requires manual lubrication. I do not know the age of your motor; however if it has been neglected and not lubricated for many years, could the sleeve bearing lubrication have dried up causing excessive wear? Can you detect any lateral or axial free play in the rotor? If so, maybe the motor needs to be replaced. The Emerson 8100 1/3 hp motor might be a look alike clone to replace yours. Contact the following link to be sure:

Replacement Motors

Good luck my friend.
 
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Old 12-30-11, 07:55 AM
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Nice movie!
Playing devil's advocate (as Irig's diagnostic is a good one), I would suggest that the noise could possibbly be "electrical chatter", of the kind you get when a motor is having a hard time picking-up speed to the point where the centrifugal switch disengages the start winding.

I wonder if perhpas all that is happening here is that the belt is a bit too tight. Try loosening it a bit and see if that helps.

You may even have a defective centrifugal switch here. The motor sure looks old.
 
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Old 12-30-11, 09:29 AM
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Thanks Irig and Pflor for your responses.

This unit was installed in October 2003. It is only used in the Winter for heat and not for A/C (that we don't have). I didn't lubricate it for the first 4 years, but have every year since, using a few drops of SAE20 oil in each end. There doesn't seem to be any play in the shaft either axial or lateral.

The actual blower fan shaft is sealed and doesn't appear to be serviceable, but it rotates just fine and doesn't create any mechanical noises.

Before securing the motor back in place I had run it without a load and there was no unusual noise. So here's my question, what would be the correct tension on the belt? It doesn't appear to me to be overly tight right now but I don't really have any reference other than "when squeezing the belt you should be able to easily move it an inch" or something to that end.
 
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Old 12-30-11, 03:17 PM
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What should the belt tension be is not an easy question to answer (without getting finger cramps), but there is something you can do:

You first need to look at the nameplate and write down the "Temperature Rise" information. You also need to drill two small holes, large enough to allow the sensing element of an accurate thermometer to fit through. One hole on the supply duct, a second one on the return. And of course you will need a thermometer

Get the furnace running and let it heat up the house for at least 5-10 minutes, until it reaches what is called "steady state" (make sure you set the thermostat to a high enough setpoint, just so the furnace doesn't turn itself OFF in the middle of your test).

Proceed then to take the Supply and return temperatures an subtract one from the other (Ts - Tr). This is your split or "temperature rise".
If the split is lower than the maximum allowed (as per nameplate), you can loosen the belt a bit (of course you'll need to turn the furnace & blower OFF before you do that).
Then turn the furnace ON again and give it a few minutes before taking a new set of Ts & Tr readings.

If your split is still below the max. called for on the nameplate, and the motor is still making that heinous noise, you can go ahead and loosen-up the belt a bit more...on and on again, until the noise dissapears.

DO NOT loosen the belt to the point where the split you measure is greater than the max. shown on the nameplate.

And thinking obvious (but often ignored) things first, make sure that the two pulleys are aligned properly.

If this procedure does not fix the noise, you might have a bad centrifugal switch in the motor (that's what the noise appears to be from watching the video), or a bad fan wheel.
The funny thing is, the unit is not that old and only being used in the winter. You should not have to deal with malfunctions like this until much later in the life of this appliance.

Please tell me one last thing: does this noise only happens when the motor starts?
 
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Old 12-31-11, 06:26 AM
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Thanks Pflor - The noise only happens when the fan starts, though I think I can hear a slight buzz that doesn't sound like it should be there whenever the motor is running.
I'll explain my set-up first and then I'll try to figure out the supply and return temperatures. I don't know what name plate to look for the info on.
I have the following wood furnace Benjamin WK400 with the optional blower attached to the side (if you open the pdf brochure you will see my set-up in the last illustration). To complement this I have a Thermolec 15kv Plenum heater that is connected to the main thermostat and is used as our main source of heat during the fall/spring and days above -10C in the Winter. We use wood when the temperature goes below that or if we need to get humidity out of the air.
So basically the cold air return comes into the blower and then is blown around the firebox and heat-exchanger and up through the plenum at which point it is heated by wood and/or electric.
All this to say that the temperature of the air in the plenum depends on whether I'm using a fire, electricity, or both. The ducts can go from comfortable to the touch, to too hot to touch.

As far as pulley alignment, I aligned by eye and then semi-tightened the fastening bolts ran the fan for a few seconds figuring that it would self-adjust for any small amount. Then tightened the bolts securely.
 
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Old 12-31-11, 01:06 PM
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We sure are not dealing with your average furnace here.

Your note that says that the duct could at times get "too hot to touch" sure is a heads up!

I don't suppose you have there a especially designed blower wheel, and the bearings quite possibly cannot take too high a temperature too well. It could mess up any bearings actually.

Now that you have shared more information the picture is more clear. The continuous noise you hear (muffled) could very well be the bearings being on their way out.

My recommendation on the Temperature Rise no longer applies here, as you don't have a traditional furnace in your house. As a matter of fact, loosening the tension in the belt could make the air too hot, something which is not safe.

I'm not sure what to recommend you here. better to call the manufacturer, they probably have dealt in the past with situations similar to yours.

Sorry!
 
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Old 01-01-12, 04:42 AM
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Thanks pflor. I'll check with the manufacturer.

Happy New Year to all DIYers!
 
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Old 01-22-12, 07:46 AM
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I have changed the blower motor and things are running much better. The motor was getting louder and louder with a constant whine, so I went into town and picked up another motor (this one is a GE that was on sale 30% off).
Now that I have removed the other motor I was wondering if there is a way to rebuild it. I haven't done anything yet, but it appears to me that something happened to the rear bearings (not the one at the pulley end). There is oil on the casing that I believe must come from the bearing.
The motor still runs and I could probably use it for something else, but would like to "tinker" with it and fix it up as a spare if I could.
Any ideas on where I could start with this, I thought here would be a good spot as the motor details are already at the beginning of the thread.

What else would one do on a -24C Sunday morning
 
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Old 01-22-12, 08:01 AM
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I do not have any advise on how to refurbish the old motor; but, a refurbished motor of that size could be used to power a belt driven bench grinder like the old Sears Craftsman model I have in the basement.
 
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