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  1. #1
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    Burning Smell from Trane XV90

    We have a 2007 Trane XV90 gas furnace. My wife started noticing a burning smell throughout the house this morning, and when I came home around 5, I realized itís coming from the furnace since the blower motor stopped working. A few questions:

    1. Given that itís Friday night, an emergency HVAC tech who mostly supports Lenox furnaces diagnosed that the ECM motor is bad and quoted me $ for a replacement motor that he will order from the Trane dealer. I see the same motor and module on Amazon for half that ó why would there be such a discrepancy? And what is the etiquette for asking why itís much cheaper on Amazon?

    2. Should I be worried about having cracked the heat exchanger since no air was running across it? It seems like the thermostat was calling for heat the entire afternoon and I guess the burners were firing, but there was no air being pushed across the heat exchanger for multiple hours, which probably explains the burning smell throughout the house. I donít want to fix the motor only to have to also replace the heat exchanger; it may make more sense to get a new furnace at that point.

    3. Since the furnace is 12+ years old, the technician said I should consider spending a little more to get a new furnace since other parts may go bad soon and furnaces only last 15-20 years. Iím curious what other professionals think, particularly if there is a risk that the heat exchanger may have been compromised since the furnace was on 5+ hours without a working blower fan.

    Thanks for any thoughts you can provide.

  2. #2
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    Furnaces have high limit(s) protection controls to shut off burners once a certain temperature is reached in the HX. They test HX in environmental chambers at the factory far exceeding what you experienced for durability and reliability. Certainly it’s worth having a reputable contractor check the HX ( heat exchanger ) The smell easily could be from the motor itself, as your still suppling voltage to it and it’s trying to run.

    Didn’t this tech have a emergency motor to install to get you going while ordering the OEM one?

    What did the tech. say about the HX when he/she was at your residence? I mean if the tech. ordered a motor then he/she determined the HX was OK yes/no?

    What does the service invoice say?

    What parts don’t get marked up in any profession?

    At a minimum that HX should have a 20 year manufacturers warranty.
    Last edited by Bazooka Joey; 12-07-2019 at 12:34 PM.

  3. #3
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    Aug 2002
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    the cost of the motor is one thing, the labor to install it, troubleshooting to find the reason it failed, warranty. What does that $15 burger cost?

    As far a replacing that a different story, you've probably hit the low end of the life span but no reason to replace right now. Plain on that later!

  4. #4
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    Gladstone, Oregon (Portland)
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    Ya. Double the cost of the part is a very fair deal, a lot less than me.

  5. #5
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    Dec 2019
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    Thread Starter
    Quote Originally Posted by Bazooka Joey View Post
    Furnaces have high limit protection controls to shut off burners once a certain temperature is reached in the HX. They test HX in environmental chambers at the factory far exceeding what you experienced for durability and reliability. Certainly itís worth having a reputable contractor check the HX ( heat exchanger ) The smell easily could be from the motor itself, as your still suppling voltage to it and itís trying to run.

    Didnít this tech have a emergency motor to install to get you going while ordering the OEM one?

    What did the tech. say about the HX when he/she was at your residence? I mean if the tech. ordered a motor then he/she determined the HX was OK yes/no?

    What does the service invoice say?

    What parts donít get marked up in any profession?

    At a minimum that HX should have a 20 year manufacturers warranty.

    Thanks for the fast response Bazooka Joey. The tech just diagnosed that the motor was bad and stopped there. To be fair, it was a late night ďemergencyĒ call, but he didnít really look over anything else, which would have provided some peace of mind. Apparently the unit requires an ECM motor, which is why I guess itís so expensive and wasnít part of his usual stock of motors. I got another quote today from a local Trane HVAC dealer, and like you said, he thinks the smell is probably the motor; he also quoted me a similar price for a replacement and told me my unit was grossly oversized and kind of Frankensteined into the plenum, so Iím weighing the cost of a new motor against the cost of a new, appropriately sized unit.

  6. #6
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    Dec 2019
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    Thread Starter
    Thanks for the reply pecmsg. Youíre right about the markup - makes sense.

    I had a second HVAC professional come today and he said the furnace looks like itís in good condition but grossly oversized (12k BTU when I should be at 8k). His recommendation was to base my repair v new decision on how long we plan to stay in this house - if weíre staying longer, it may make more sense to buy a new one. I appreciated that kind of realistic, non-sale pitch answer. Thanks again for the reply.

  7. #7
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    The Tech. probably was basing the size ( Furnace ) you need on a somewhat educated guess, the better way to determine what size you really need is by a load calculation. The existing ductwork may also be a incorrect size. There are calculations for that also if you do decide to replace the furnace down the road.

    From what was found that furnace ran its course and stopped production in 2008, rated at 93% which isn’t to shabby, albeit oversized.

    The XV90 was Trane’s top-of-the-line condensing gas warm-air furnace until it was discontinued in 2008. (Current top-of-the line models include the XV95 and the XC95M). The furnace was Energy Starģ rated with an AFUE of 93% or better.

    The 12K and 8K you mention guessing should be 120K and 80K

  8. #8
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    Aug 2002
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    I wouldn't consider replacement right now. Is it oversized............Probably just like the ducts are undersized. Bad duct design leads to ECM failures but 12 years is a good run so don't make hasty decisions.

    Replace the motor.

    Have a manual "J" performed to find out exactly what size furnace you need.
    Have a manual "D" preformed to find out how many CFM's the ducts can handle.

    Line up your contractors and have a game plan set for what has to be done and how. Replace in the spring!

    Also consider a blower door test to find out how you can tighten the envelope and further reduce the furnace size!

  9. #9
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    Quote Originally Posted by Rob in NJ View Post
    I see the same motor and module on Amazon for half that ó why would there be such a discrepancy?
    I was at the Movies last night to watch Frozen II with my grandson, popcorn was $8.00 for a medium butter popcorn, this morning I saw it at Krogers for .29 a package, why would there be such a discrepancy?
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  10. #10
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    Aug 2009
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    I don't know if you were priced just the motor or the module also bu tif the module was included it needs to be programmed. I don't know if Amazon would have the equipment or software to program it. If it is purchased elsewhere do you think the distributor would program it for free? Just one of many reasons for pricing differences.

  11. #11
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    Dec 2019
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    Thread Starter
    So the problem ended up being a burned out SG379 Thermistor on the blower motor fan module - I think thatís what was making the burning smell. I ended up replacing the thermistor with a new one from Amazon and the system is up and going again. Thank you everyone for your feedback and help!

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