Furnace Trane XE90 blower not spinning

[Vikas]

But makes horrible humming noises when applied power. Blower will spin freely and smoothly when there is no power applied to it. I can watch the blower and it does want to spin in the correct direction but it is only crawling, like one degree every few seconds. Trying to push it by wooden stick shows lots of resistance as if there is a giant magnet holding it back. Start capacitor was replaced but that had no difference in the symptoms.

I checked the motor stator windings and they all checked out (4 - 6 ohms). I checked the voltage coming out of the controller when it commands the motor to spin. No load voltage is 120VAC and when the motor is making the noise, it is at 118VAC. I also tried all four leads and they all noises, some more some less.

When the motor spins freely without power, there is NO axial or lateral play. When the power is applied, I do not see any shift. This tells me that motor is mechanically sound. I am at a loss as to what can electrically go wrong with rotor on this type of motor. I am under impression that they are pretty much bulletproof.

I am concluding that I need new motor and motor only i.e. the fan assembly is fine (because it spins freely without power) and controller is fine (because it is providing 120VAC to the motor).

I would like to apply direct 120VAC to the motor but I do not like the unsafe aspect of it. Given that I have already measured the live voltage to the motor coming out of the controller at the junction and it is showing 120V, there is no logical reason to think applying direct wall power would make any difference. Can you come up with a scenario under which this assumption would be wrong?

As you can imagine, the house is very cold. I already had a technician come in and the motor is on the order. But I definitely want to make sure putting the new motor is going to fix it. I just can not take "oops, we need more parts and they need to be ordered" saga anymore.

[Trane XE90 forced hot air, installed YR2000]

 

[abycat]

I would bet a new motor would fix it but im pretty sure the brushes are messed up.

 

[meangreen01]

Yeah, sounds like motor is toast. I'm surprised though that the motor had to be special ordered. Normal direct drive A/C motors can be replaced in 99% of application out there by carrying 2 universal replacements and a belly band adapter on the truck. If they're not stocking such basic repair parts like that I'd question the quality of the HVAC Co you're choosing to do business with. Don't know how cold it is up there, but even if your motor fell into that 1%(which it doesn't sound like), in cases of severe cold we could source a motor using the distributor's on-call service.

 

[Vikas]

I am almost certain this is a single phase induction motor with multi-tap windings. They don't have brushes or slip rings (as far as I know).

Some of you might know their induction motors well. Can somebody explain me the failure mode? I have done google research and I have not come across similar failure on a single phase induction motor.

Is it worth it trying to take the motor out myself and see if I can put back life in to it? It is little bit more complicated than I would like and I am suspecting that there is nothing that I can do to fix it and hence I am resisting the urge to start tearing it apart.

- Vikas

 

[Quest]

the blower motor is toast.

Q.

 

[Trav]

Does it have a capacitor?
Have you tried turning it with power applied and its humming?

 

[Vikas]

Originally Posted By: Quest
the blower motor is toast.
Q.


Can you explain it though? I graduated as an electrical engineer from one of the best university in the world but I have forgotten everything that I learnt there :-(

 

[meangreen01]

These types of motors are not of particularly high quality. They are engineered to a price point, which in the case of your motor, is maybe $50. They utilize sleeve style bearings, which over time will fail in some sort or another, and that appears to be your problem.

Sorry, I can't share any further insight than that into various motor failure issues. I've replaced hundreds of motors like yours, and once troubleshooting led to a motor not working, it would just get replaced. Remember. we're talking about a $50 dollar item(although, that's not what it's gonna cost you, unfortunately). To break it down and start rebuilding a motor of such low value just doesn't make financial sense. Larger motors in industrial apps and such that cost 10x as much or more- yes. Fractional HP Direct Drive motors- no.

Sort of like your auto mechanic diagnosing a bad battery or something. Once it has been determined it's bad, it's not like they are going to tear into it to see what failed inside it. That's where you engineers step in. Above our pay grade and all that LOL.

 

[Quest]

Hi Vikas,

Is yours the traditional AC motor (1/4 hp) or yours on the new variable speed type? If it's variable speed type, pull the connector off and test all the coils 1 by 1. tyically measures around 4ohms typical.

If yours an AC variable type, provided that all the coils tested ok and the spindle turns freely, your other problem maybe to do with the controller board.

10yrs is just about what you can typically get out of these Trane controller boards.

See if the driver section is burned out and see if you can repair them and save money.

My take is 50/50 chance (50% chance goes to the motor; 50% goes to the board).

Q.

 

[Quest]

If my search is correct, your controller board should be CNT05165, which sells for around 120bux on ePrey (typical):

http://www.ebay.com/sch/i.html?_nkw=Tran...6.c0.m270.l1313

Given the fact that there are no high power bipolars, FETs, etc. to drive the motor (if you look at the board components carefully, mainly the processor and some relays, and a few capacitors (DC filtration or bypass?), there isn't much on them.

That's why I gave your furnace a 50/50 chance of either a board problem or a blower motor problem.

If the controller board contains high power bipolars (motor driver) or similar, then I would insist in checking out all the drivers first and see if they are faulty (serviceable) or not before proceeding to the motor.

I personally do not blame the motor haphazardly; but then again: anything can happen to a motor these days..

Take care,

Q.

 

[Vikas]

Hold on a second here! If there is 120V being delivered by the controller board, how can it be at fault?? It is CNT03076

 

[meangreen01]

Originally Posted By: Vikas
Hold on a second here! If there is 120V being delivered by the controller board, how can it be at fault??


It isn't.

 

[Vikas]

Alright; I finally had the courage to hot-wire the motor bypassing the controller and sure enough it makes the same horrible noise.

OK, so the motor is toast.

Thanks guys! Now I just have to hope that the guy bringing the new one brings the correct one. It is going to cost me a lot but at least with the replacement motor, the house should have the heat back on.

- Vikas

 

[JimPghPA]

If the wiring in your house is good, you could go to Wall-Mart and get about 12 to 15 low cost heaters to keep the house warm enough to live in until you get the blower motor fixed.

The plastic heaters with a low and high usually run 1K Watt on low and 1.5 K Watt on high, but on high the plastic smells so I only use low.

A few years ago, I picked up 13 of them in the spring when they reduce the price to get rid of their winter stock. I thought they would be a good back up heating system if the gas line in the street ever had a problem. The furnace heat-exchanger went bad under warranty about a year ago in the winter (the CO detector showed the problem) and we used the electric heaters for several days until the furnace was fixed.

If you go with the electric heaters plan on two for each lager room, and one for each small room. If you have a cellar that is a large open space, you will probably want three to keep it somewhat warm, and also to add enough heat so the rest of the house does not get too cold.

 

[meangreen01]

When they bring the new motor check to see if it has oil ports on it. Like so many other things, oil ports that used to be standard went away in the name of low/no maintenance. Virtually all OEM motors have been sealed for 20 yrs or so now. Some replacements motors have them. It helps longevity to have the ports for yearly oiling, although I've seen bearing issues even with properly oiled motors.

 

[Vikas]

That is one of the reason I have been trying to find out what went wrong with this motor. I know it is not the bearing and it is not the winding. What else is there in a motor to go wrong??

I picked up few electric portable heaters on clearance from Target at the end of the season few years ago. I bought about 5 of them and heard from the "boss" as to why I did that! I think now she must be glad that I did that

- Vikas

 

[Dave Sherman]

Originally Posted By: Trav
Does it have a capacitor?
Have you tried turning it with power applied and its humming?



I'm surprised only one person brought this up. The symptoms point heavily toward a failed capacitor. Unless it's some fancy variable speed motor, most furnace blowers are just single phase induction motors with a run capacitor. Maybe with different speed windings, but there's usually a capacitor for the start winding.

Look for the capacitor, just a metal can with two terminals in the motor wiring, and replace that first. Better to spend the $10 or so on a new capacitor then just go right for the $100 motor, which still won't run with a bad capacitor.

 

[Quest]

Originally Posted By: Dave Sherman
Originally Posted By: Trav
Does it have a capacitor?
Have you tried turning it with power applied and its humming?



I'm surprised only one person brought this up. The symptoms point heavily toward a failed capacitor.



@ Dave:

Please re-read Vikas original posting : ".... Start capacitor was replaced but that had no difference in the symptoms...."

Capacitor has been replaced already.

Also: Vikas already tried the trick of pushing it with a stick...



Q.

 

[Dave Sherman]

Originally Posted By: Quest
Originally Posted By: Dave Sherman
Originally Posted By: Trav
Does it have a capacitor?
Have you tried turning it with power applied and its humming?



I'm surprised only one person brought this up. The symptoms point heavily toward a failed capacitor.



@ Dave:

Please re-read Vikas original posting : ".... Start capacitor was replaced but that had no difference in the symptoms...."

Capacitor has been replaced already.

Also: Vikas already tried the trick of pushing it with a stick...



Q.


D'ohh... Thanks, I had missed that detail

. My mistake, I concur that sounds more like the motor is kaput.

 

[Vikas]

Indeed, the motor was replaced and now everything is fine. I am also surprised how quiet the new one is. I suspect the old one had been slowly dying for years based upon the noise and vibration that I used to think were normal.

The motor is *very* heavy. It is 3/4 HP. The old one was GE, the new one is generic and Made in Mexico. One of these days I am going to open the old one to see what kind heavy rocks have been stuffed in to it

- Vikas