Payne Plus 90 - Inducer Blower Hot?

[Alley Oop]

This Plus 90 with a Chromotherm III is tripping the aux-resetable limit switch on the main blower housing after a few minutes, and the only thing I can find is the combustion draft inducer blower motor heating up, as in hot to touch the case. That motor is thermal protected/limited to 40 degrees C (104 F) ambient. The thing doesn't make any bushing noise, and I can spin the motor freely with a tweaker through the case vents. There is maybe 1/8 or more shaft end play. The blower control card is good, ICM replacement, same condition with original type card.

If I reset the limit switch, set the thermostat, and supply AC, I get a normal ignition cycle, and maybe 5 minutes of heat before the thing shuts down again.

There was a recent windstorm with power outages, and the unit was shut off at the AC supply switch after it went cold and the blower stuck on when the power came on. It worked normally until then.

Ideas? Other conditions which might cause the inducer blower motor to overheat? Barking up the wrong tree?

Thanks,

Alley Oop

[contactor]

A lot of things could cause it to trip. You need a good tech to diagnose it. No simple answer . Get checked ASAP.

[Alley Oop]

Allrighty then, lots of things do not appear to be the problem, and a hands-on second opinion is not an option. Would someone else a bit more helpful care to hazard an opinion on why that motor might heat up other than the motor developing a problem, as in windings? It seems excessive load is unlikely, but that's the reason for the question.

The inducer blower motor overheat condition does not have very limited causes? The pressure switch is functional, there is no indication of a furnace overheat condition, no indication of excessive condensate or of soot, (as in diminished exchanger capacity or plugged lines), no other switches are tripping, the controller card is good, is not blowing the fuse, blower delay setting is sufficient, and there are no known indicators of thermostat issues.

I'll go back through the schematic, but I don't want to tear this thing down further than absolutely necessary.

Thanks,

Alley Oop

[Alley Oop]

My understanding is they don't favor step by step how-to questions for DIY here, but I did not realize asking a question is a violation of policy or rules. So do only HVAC licensees get their questions answered here, and are forbidden from answering the questions of others? If I missed something, is there a site known to anyone here where people do freely discuss this type of question?

It wasn't exactly a blind question, or a request for step by step procedure, from my humble perspective. I have never run into a repair of a common home appliance or system where accurate unit specific technical information is so difficult to find and reference, or parts so hard to get. Do public libraries have the manuals? What is the reason for all the apparent secrecy or protectionism, if I may ask? These systems really don't seem so simple that folks are going to lose a lot of business by helping people or encouraging a little transparency. Many other technical repair fields heighten public confidence in their profession by disseminating technical information. I'm grateful to have the opportunity to read and learn here, but that doesn't exactly get a furnace working in the dead of winter in a lean year, know what I mean?

So just in case commoners are allowed here, and reply by the pros IS discretionary as opposed to verbotten, I ran the thing a couple of more times, and that inducer blower motor did screech on cold start-up, so I drilled a very small hole in the end bushing cap and lubricated the bushing, first with a PTFE spray, then oil. I got it through a 2 degree cycle of maybe 10 minutes to auto shut down after that, but that motor was too warm again for my liking. I probably need to get at the bushing on the blower end of the shaft and lubricate that if I'm going to use it, but may need to jerk it and ohm the windings.

The main limiter switch on the burner housing is not what is tripping the auxiliary switch, the inducer card is functional, SOMETHING is tripping the aux limit switch on the main blower housing, the inducer motor is thermal limited, the blower/control card is good, and it looks like I might need an induction blower motor.

OK then, sorry if I wasted anyone's time, or broke the rules. As you were.

Happy New Year.

Alley Oop

[Mr Bill]

If you had a storm your roof jack did not get bent or stopped up by chance did it? it could have caused the vent pipe to be partially stopped up might cause the inducer motor to overheat.

[Mr Bill]

that inducer blower motor did screech on cold start-up, so I drilled a very small hole in the end bushing cap and lubricated the bushing, first with a PTFE spray, then oil.


Could help but most of those inducer motors are high RPM like 3000 rpm's might want to use some sort of turbine oil if you have any handy.

[Alley Oop]

Thanks Bill. I will look up there, but that stack is configured to hook back down to prevent rain getting in, I reckon, so the odds are slim. I was hoping to get someone to tell me whether the thermal limiter on that motor can indeed trip the aux limit switch, or whether the motor drawing excessive amperage can do that. I used ATF in that bushing, but do have some oil around here that is turbo rated. I guess I should vaccuum clean the secondary and the line while I'm in there, but hate to tear into it if I don't need to.

Your handle and title look official. Please also let me know if I'm afoul of the rules here, as I would like to preserve access to the resource, and just sort of stumbled in here through Google looking for answers.

Thanks,

Alley Oop

[4l530]

Hmmmmm.
So an auxillary limit switch on the blower (circulator) motor is tripping (NOT the main limit between the heat exchanger cells),
And you find that the draft inducer motor feels hot...but not to the point that the thermal limit in the motor takes it out...and no mention of any apparent drag on this motor.

What have you done to this furnace??

Sounds to me like there may be two separate problems.

No offense, but you really ought to have a Tech look at it.

[4l530]

By the way, you're having trouble getting information and / or parts for this furnace because it's just way too easy to make any number of mistakes that could be very detrimental to the furnace, life, limb, or property.
The manufacturers don't want to take the liability for that. No one else does either.
It's one thing if you've been trained on them, but some people will try anything without knowing enough about it.

[Alley Oop]

None taken, and thanks. Distinct possibility, another problem exists. Maybe I should be cleaning the secondary heat exchanger, checking for condensate and algae, or even vacuum cleaning the primary, run some alcohol through the line, but the clear line to the pump is pretty darned clean, and no signs of soot. I really hate to tear the thing down, being a novice and all, but will if I find I have to. Practice makes better. Like I said, an HVAC tech isn't an option at present, purely economic necessity. I haven't done anything to it ever, yet, excepting change out a blower/control card that the manufacturer wasn't real proud of to begin with, matching the blower delay, and of course keep the EAC clean. Believe me, I would educate myself quietly if I could simply access a repair manual.
Just saw the second post, 41530. Yea, I figured the safety factor would come up, but I've played with enough truly dangerous devices and machines from Uncle Stupid to high voltage and beyond for a living in my time, to make a little gas heater look pretty tame. I'm not really into being protected from myself, and have done more things by the numbers in life out of necessity than most. I've also earned enough technical certs that I'm not exactly intimidated by man-made stuff I haven't torn down before.

Alley Oop

[4l530]

http://www.free-smiley.info/scared/scared.gif egads man!


What you say you are contemplating doing is a buttload of work to a furnace that was cheap to begin with, that I'm not sure would do anything to help.

I understand about the financial thing, and the past experience. But if you would only call a Tech, you could at least get an opinion at to what it does need, from someone who could examine the problem closely. And not spend New Years Day cursing at the screws that strip out in that heat exchanger.

[fixitmanmc]

upflow, downflow, or horizontal? upflow & horizontal, ck temp in blower chamber, if ok the limit may be bad

[danielworkerbee]

EAC you say, been keeping it clean ?, how old is the unit and how long have you lived there ? luck dan

[Alley Oop]

Downflow, fixitman. I have been wondering about the aux limit switch being weak. I realize the thing is also wired into the main limit switch, but I ran it with the cover off a couple of times to run some tests, sucking cool air out of the utility porch, and it still tripped the aux limit. I fired it up for a test this morning and ran two degrees through a normal cycle without tripping the aux limit, but shut it down after that, when I heard some relay chatter going back into the ignition cycle. I want to be sure I find the problem(s) before putting it back in service. Because I am pretty sure there is no overheat condition and nothing tripping the main limiter on the box, I thought about bypassing the aux switch for monitored test purposes only, but don't want to damage anything.

Dan, I put that thing in around `87 when I re-insulated and got rid of baseboards,and have been here quite a while longer. It hasn't always been worked hard, since I generally heat with wood through fall and spring, and supplement in winter. I'm at 70 degrees in the main room on wood right now, but the fire doesn't always get stoked when I'm gone, the better half can't pack wood or put the big rounds in, and I'll need to do a day or two of cutting, splitting, and hauling in what I have down and seasoned pretty quick if I don't fix this furnace. Working on the furnace sounds pretty good with freezing rain and 30+ naut wind this week.

Thanks,

Alley Oop