Furnace blower motor dying - what to do?

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rationull

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Early this morning my wife and I awoke to a slight burning smell and went downstairs to investigate. I found the furnace box hot like it had just shut off and the fan box emitting a buzzing sound and the burning smell. Unplugged it and went back to bed to look at it after getting up.

Nothing looks charred so I'm guessing the burning smell was either internal to the motor or burning dust. Messing around with it, I found that the fan will still come on if I turn it (the fan) on manually. After I discovered that, I turned the heat on. After a bit I listened and heard a buzzing sound from the fan. I turned the fan on manually (which is a higher speed), it came on, I turned it back to auto, it stayed on (it should've been on in the first place at this point).

My conclusion is that the fan can't start up at its slow automatic speed. It's not all that surprising -- the furnace is 23 years old and the fan has been a little slow to start up since we bought the place a year and a half ago. Even with the manual "power boost" it still starts up kind of slowly.

I'm hoping it's just the motor, because if I can find somewhere to buy one I'm assuming I can just replace that pretty easily. I might have somebody come out to look at it anyway because I don't want to replace the fan if the problem could be in the controller (or even the thermostat?) or if the rest of the thing is on its last legs anyway.

Does anyone have any references they can recommend or any helpful info as to how I can diagnose this further or does it sound pretty clear cut? Should I just call someone? (I do have the number of a trustworthy HVAC guy).
 
Call the HVAC guy.

He can also check the unit over and make repairs.

No reason to buy a new motor yourself and hook it up wrong and burn up the new motor.
 
Considering it is safety related, I too would have it checked buy a HIAC guy. I had a burning smell once that I thought I'd fixed only to find out days later that I had a hold in the firebox. Lucky we did.t get agitated with Carbon Monoxide.
 
Well, if it's just your plain-jane, run-of-the mill, upflow, gas-fired furnace of that era, it has a fractional horsepower, direct drive, multispeed motor.

Your scenario sounds like either the motor is bad or fan control is bad. Depending on make/model, the fan control is either a mechanical switch or it could be integrated into a circuit board.

You can rule out your thermostat unless you have electric heat or a heat pump.

Expect to pay anywhere from $250 to $500 for a serviceman to replace the motor. Toward the $500 end if you call today(overtime). Around the same if you need to replace fan switch or circuit board.
 
It actually sounds like the capacitor is bad, it provides that first juice the fan needs to turn over. Watch that capacitor, it holds a pretty strong charge!

capacitors_jpg.jpg
 
Again, before casually jumping into conclusions, something we need to know:

(1) what kind of furnace blower motor is it? 1/4hp? 1/2 hp, AC 120V?

(2) is this a forced air furnace (natural gas/heavy oil) we are talking about?

(3) if (2), when was the last time you have a fully competent HVAC guy over to inspect and lubricate the unit? (inspection involves take a look at the heat exchanger, lubricate squirrel cage bushings, motor bushings, adjust the flame pattern, check/adjust the pilot light, replace thermostat if needed, etc.)

(4) if (2), is it a single stage pilot-light based forced air furnace? What age/model is it?

(5) are you competent in servicing/diagnosing AC related issues, including AC motors, condenser, etc.?

Q.
 
Originally Posted By: dishdude
It actually sounds like the capacitor is bad, it provides that first juice the fan needs to turn over. Watch that capacitor, it holds a pretty strong charge!

capacitors_jpg.jpg



Replacing just the cap on a fractional HP blower motor, even if it is bad, won't solve the problem completely.

Yeah, we don't know the OP's skill level to know if it's a good idea to DIY or call in an expert. Probably best to call an expert as even changing out a motor can get complicated if you don't know what to get at the parts house.
 
Update from my OP: After a while on auto the fan stopped working again and was buzzing. Manual mode (higher speed) still worked but the fan wouldn't run for very long at all when going slower. It seems like it's most likely the motor itself.

Reading your responses makes me realize calling the HVAC guy is the best approach for me. I'll probably call today but have him come out next week because it's not *that* cold right now (lows in the 30s) and we can crank the heat with the fan on manual before going to bed to build up some warmth. The house is well insulated. I'm told the motors have separate windings for separate speeds so it seems like if high speed works now it will likely work for a while.

To answer questions:

I have no HVAC experience. My skill level extends to replacing the filter, taking the covers off and poking around, and general understanding of how it works.

I have not lubed the motor. I'm embarrassed to say I thought it didn't have any lube points but it turns out it does call for periodic lubrication (every 5 years if run intermittently). I don't know when it was lubed last.

The furnace is a "Day & Night" (Carrier) single stage forced air gas furnace with 115V single phase 1/2 hp motor. AFAIK it's 23 years old. Not sure what the exact model number is but if it's useful I could figure it out.

I had a couple simple inspections of the furnace when we bought the house a year and a half ago for safety but haven't had as detailed an inspection as Quest suggests. Sounds like a good idea.
 
Hi rationull:

Thank you, that's very detail of you.

A great man is one that knows his limitations. I certainly know/aware of mine.

Sounds like your motor is on it's way out, so replace the capacitor may or may not work to you favours, afterall (if it costs a few hundred dollars to replace, then yeah, consider other options e.g. a used single-stage furnace from craigslist that are a few years old and comes with all the parts and so).

a 23 yr old single-stage forced air furnace, IMHO, is just about to go out (typical 1-stage forced air natural gas furnace heat exchanger are of 20 to 25 yr warranty, so don't try to push your luck on that unless you are in a financially desperate situation.

If you can find one (used single-stage furnace, or a brand new one if you state/region allows per bylaw), then it makes good sense to replace the whole unit instead of servicing just the motor.

Otherwise, if you are financially stressed, replace the motor only. Get a GE motor if you can of same HP.

Take care,

Q.
 
Many newer furnaces have permanently lubricated bearings on the blower motor, so you can't lube them anyway. If you have a decent motor shop nearby you could pull the whole blower assembly and have them put in another motor & wire it up for you (as long as it has a plug-in connector). Don't be surprised if you have trouble getting an OEM motor from Carrier for a 23 year old furnace, and BEWARE the upsell of an HVAC guy on a new furnace because your old one is "junk"-if you know your tech you'll probably be OK. Too many companies pressure their techs to sell unnecessary new systems-"stealerships" aren't confined to the auto industry.
 
If the furnace really is on its way out then I think we'd be inclined just to replace the whole thing, although I don't know if that means we'd be without heat longer. We're not in dire financial straits or anything so if we need to do that we should be able to.

I am aware of the upsell strategy. When we moved in here, I had a guy from a local chain come out. He took one look at the furnace and I think dollar signs flashed in his eyes. He effectively told me it was on its last legs and IIRC implied it wasn't even safe to run. He started it up and after waiting not quite long enough for the fan to come on declared that the fan wasn't starting up like it should. He wanted to sell me a new furnace, but apparently not bad enough to remember to send me an estimate on replacement like he said he would.

I was a little worried and didn't really want to spring for a new furnace immediately after buying the house if I could avoid it, so I got a couple more opinions. I had another guy who had been recommended by an acquaintance come out and he seemed to think with a little cleaning and TLC it would be fine. For good measure I had the gas company come out and inspect it to (they'll do it for free) and they had no problem with it either.

It's the second guy who I'm gonna have out this time, needless to say. It's a small local family shop, not a chain with a bunch of "techs".

With this advice I won't be too surprised if he recommends replacing the whole thing though.
 
A quick check you can make:
- turn the power off to the furnace
- remove upper door
- remove lower door
- grab a flashlight or trouble light
- reach in on the left side of blower housing and spin the squirrel cage
- squirrel cage should spin freely several revolutions. If theres any tightness or it stops quickly, it's toast.
- If it spins freely grab the shaft that comes through the center bore of the squirrel cage and check for play in the bearings. In/out is OK. Side to side it's toast.
 
23 years is about all you should expect from a furnace. It is time for a new one.

In the mean time, turn off the power, Check that the mount for the motor is not broken. Most mounts are part of the motor, and you have to get a new motor if it is broken. In your case with 23 years it would be wise to just get the new furnace. If the mount is ok, loosen the screw for the squirrel cage, remove the squirrel cage. Be sure you do not bend the center section of the squirrel cage. When you pull on it pull evenly so the center is not bent. Put some very light oil on both ends of the shaft for the motor. Some of the light stuf that you get in a spray can from hardware stores is good for fractional HP motors.

Probably want to take your time to look for a new furnace sometime soon.
 
If I spin the squirrel cage lightly by hand it only spins for 1/3 to 1/2 a revolution. Motor mount seems fine and there doesn't seem to be any play in anything. The sticker on the motor says to lube it with 20 wt non detergent motor oil.

Given that it runs on high speed but not on low speed, I'd been assuming it was internal to the motor but I guess it could just be too sticky to move at low speed? Or maybe it *was* and now it's burned out.

At any rate I've got an appointment Monday morning to get it looked at. If we need a new one we can probably just tough it out for a little while until we can find a decent deal on a new one considering it's almost March.
 
Well 20 years is about the ave life expectency for furnaces. That said, Carrier IMO are the best residential furnaces out there, and living in CA I would assume it's lived a comparably easy life, so I wouldn't be resigned to the fact it needs to be replaced.

A motor installed on straight time will prolly run you about $350. A new high efficiency furnace will run you from $2000 and up. Many states and even the Fed offer rebates or tax incentives on HE furnace and A/C's that softens the blow.

Other factors to consider: are you sure it's 23 yrs old? You can tell on Carrier products by looking at the serial #. It's on a label on the side or bottom of the upper compartment. It'll be a 16 digit number with a series within indicating date of manufacture xxxx 0490 xxxx xxxx was made Apr. 1990. Is it a high efficiency? Carrier's been making HE since 1984, and if you already have one, there's not much more efficiency to be had with the new models. Easiest way to tell that is if it vents with PVC= HE.

Have the tech give you his expert opinion of the unit. If he's honest he'll tell you wether it's worth sinking a few hundred bucks into or better to get a new unit. IMO, I'd stick with Carrier products(Carrier, Bryant, Payne) if you replace.
 
to each his own but when carrier sold out to icp their quality went down to the bottom of the barrel day and night bryant kenmore carrier and many other off brands are all the same with a different logo matter fact if you buy a icp unit you can pick what lbel you want . rheem trane american standard or lennox imo.
 
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