Blower Motor Tries But Can't Turn

Discussion in 'HVAC' started by wlr211, Feb 11, 2010.

  1. Feb 11, 2010 #1

    wlr211

    wlr211

    wlr211

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    I have a very old gas, forced air, Luxaire furnace model #GH102SE and am trying to limp through one more winter season.

    The blower motor can not turn the squirrel-cage fan. I can manually move the fan belt and the fan easily turns. But when the motor receives the signal to start, it jerks the fan belt and fan into action but immediately everything stops and the motor makes a buzzing sound. I've tried to manually move the fan belt when the motor is making the buzzing sound and it feels like the system is frozen.

    The motor is about 10 years old and I replaced the fan's axle and bearings last season, beginning of 2009. I also replace the original thermostat with a Honeywell digital thermostat last year. The pilot light seems to be functioning properly and the burners ignite and stay lit.

    From my description does it sound like the motor is bad? Should I disconnect the fan belt and see if the motor can turn? If it does what would that mean?

    Any help would, of course, be appreciated.
     
  2. Feb 11, 2010 #2

    Bud Cline

    Bud Cline

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    Is this motor a "capacitor start" motor?
    Does the motor have a small dome-like cover perched on top of the motor housing?:)
    More than likely it's a bad capacitor.:D
     
  3. Feb 11, 2010 #3

    wlr211

    wlr211

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    Wow Bud, thank you for the very quick reply. I really don't know enough to know if it is a "capacitor start" motor or not. I don't think there's a dome-like cover on top of the motor but I'm going back down to the crawl space to have a look right now.

    I've been reading about capacitors and it would seem that, if I have one, that might be my problem given the fact the motor isn't really all that old. I'll report back when I have more information.
     
  4. Feb 11, 2010 #4

    Bud Cline

    Bud Cline

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    I'm not an expert and I don't know that much about electric motors either but I did major in that type of thing in high school many decades ago. A lot has changed since then I'm sure but if my memory serves me correctly (and it doesn't do that so much anymore) I'm feeling a capacitor issue here. If the motor does not have a capacitor then we have already exhausted my knowledge of the subject.

    My recall is that capacitors are used to start a heavily loaded motor and get it to a certain rpm at which time the capacitor leaves the circuit and the motor runs on its own with less need for the added assistance. It takes more juice to start an electric motor than it does to run one. Once the initial start-up load/drag has been overcome the capacitor is no longer required.

    Doesn't sound to me like the motor is able to reach the "run" stage.

    Hopefully someone here will come along with more knowledge than I have about such things.

    In high school I built an electric motor from the ground up. I personally hand wound the windings and all that stuff and the damned thing actually worked. To this day I remain impressed with my ability in that field. But, that's as far as it goes. You now know what I know.:)
     
    Last edited: Feb 11, 2010
  5. Feb 11, 2010 #5

    Wuzzat?

    Wuzzat?

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    How old?
    25 years +/- 3 years is avg. for "resi. HVAC equip."

    A buzzing sound may mean a bad connection. See what the motor voltage reads during the buzzing.

    Does your motor look like this?
    http://www.hvacrheritagecentre.ca/exhibits/collections/images/artif_283.jpg
     
    Last edited: Feb 11, 2010
  6. Feb 11, 2010 #6

    Bud Cline

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    Strummin' my fingers on my desk top waiting for this cliff-hanger to end!!!!:D
     
  7. Feb 11, 2010 #7

    wlr211

    wlr211

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    Bud, this cliff hanger is hardly worth waiting for but here's what I'm guessing.

    I looked at the motor and didn't see anything I would describe as a capacitor attached on it or even nearby. I disconnected the fan belt and turned on the motor. It did not work but, rather, made the buzzing sound.

    I turned off the power and manually rotated the motor pulley. It turned but was making a "crunching" sound. I then noticed that there was a very slight amount of play in the pulley. It moved in and out of the motor housing. And I also noted that I could make the pulley lock-up by pressing inward on it. As I said, the play was very slight, maybe 1/4 to 1/2 inch at the most but it would lock up.

    There is an electrical junction box on the outside of the furnace assembly that the two wire leads from the motor go into and other wires are attached to the outside. I guess these come from the thermostat. I doubt there's a capacitor inside this box but could be.

    I'm thinking I need to remove that motor, cut it's wires and replace it.

    By the way, the schematic glued to the inside of the cover door of the furnace shows a capacitor beside the motor but it say "if used" underneath it. I'm guessing not all motors for this model furnace used a capacitor.

    I'm also guessing you can stop strumming your fingers now. Thanks.
     
  8. Feb 11, 2010 #8

    wlr211

    wlr211

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    Wuzzat...just noticed your reply and yes I know I'm on borrowed time with this furnace. Thanks for posting the picture but, no, my motor does not look like that one. There is not a dome on top of the motor housing and my motor appears to be a little longer and not to have quite as big a circumference as the one you pictured. Thanks for responding to my plea for help.
     
  9. Feb 11, 2010 #9

    Bud Cline

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    OK one last guess.....and it is only a guess.

    If that motor is old enough to have "brushes" that could be another possibility. Once the brushes wear down they become small/short enough to leave their individual housings/retainers and can temporarily lock an armature and keep it from turning. The motor's commutator windings would still hum when juice was applied but the brushes wouldn't be able to deliver juice to the armature and would be in disarray inside the motor.

    There was a time when motors had access to the brushes by removing a small threaded plug on either side of the housing. Inside and under that plug is/was basically a piece of carbon and a spring and wire lead. You could pluck the brushes (carbon remnants) and replace them easily enough.:)

    OK, Now that's all I got for sure this time.:)

    Just trying to save buying a whole new motor is possible.:)
     
  10. Feb 11, 2010 #10

    wlr211

    wlr211

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    Thanks, changing brushes out may be a stretch for a man of my limited abilities but I'll take a quick look. Guess I'll also make a few calls and see what kind of dollars I'm talking about for a new motor.

    Thanks again to you and Wazzat for weighing in. As with Tennessee William's Blanche DuBois, "I've always depended on the kindness of strangers."
     
  11. Feb 11, 2010 #11

    Bud Cline

    Bud Cline

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    If by some small chance it is the brushes....
    Trust me - you can do it. Changing brushes is straight forward and easy to do. Pull the old ones out and put the new ones in. Not much different than changing the batteries in a kids toy or flashlight.

    Considering the cost of motors it's worth a shot.:)

    Let us know what happens.:)
     
  12. Feb 11, 2010 #12

    Wuzzat?

    Wuzzat?

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    Last edited: Feb 11, 2010
  13. Feb 14, 2010 #13

    Nestor_Kelebay

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    If it was me, I would take that electric motor to a motor rebuilding shop and they'd be able to tell you what's wrong with it after a few minutes of testing, and probably wouldn't even charge you for doing that. If the motor is only 10 years old, there's probably not too much wrong with it.

    But, as pointed out earlier, the heat exchangers in furnaces typically only last 15 to 20 years or so, so you don't want to be putting a lot of money into an old furnace.
     
    Last edited: Feb 14, 2010
  14. Feb 15, 2010 #14

    wlr211

    wlr211

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    Just thought I'd put a cap on this thread for anyone interested or sharing a similar problem. I ended up purchasing a new motor from Grainger at a price of $164.00 and that has seemed to correct my problem.

    Prior to acquiring the new motor I called an electric motor repair shop here in Atlanta. They wanted $85 per hour to work on the motor and I figured that, even if it only took one hour to make the repair, I would not be saving that much given that I'd have to pay for parts and allow additional down time for the repair.

    I did save the old motor and intend to take it apart and see if I can repair it. That'll give me a spare for the future. Although I'm not sure how much of a future my furnace system has.

    One slightly tricky and unexpected element to installing the new motor was the fact that some electric motors, like the one I bought, are reversible. I needed to reverse the black and red wires inside the motor housing in order to make the motor run in the direction my system needed it to run. No big deal, I just didn't know this until after I had installed the motor and realized something wasn't right. To paraphrase the immortal words of The Who, "I won't be fooled again." At least, not by that particular issue.

    Anyway, everything seems to be working as it should. I have heat and I think I got the pulleys aligned properly and the tension on the fan belt correct. And, though others I'm sure could have done this job quicker and better, I learned, once again, that some home repair projects aren't brain surgery. If one is willing to give it a shot and, in my case, crawl on his belly like a reptile through a crawl space it is possible to be one's own repairman. Thanks again to those who offered advice for my problem.
     
    Last edited: Feb 15, 2010
  15. Feb 15, 2010 #15

    Nestor_Kelebay

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    Every single phase induction motor is reversible. By reversing the leads to the start and run windings, the motor will turn in the opposite direction. Induction motors include capacitor start motors (of the kind you find in high torque applications like air compressors and refrigeration motors) and split phase motors (like you find on washing machines and clothes dryers).

    In fact, the whole design of Maytag top loading clothes washers revolves around the fact that the motor can be made to turn backward. There is something called a "motor relay" in Maytag washers that reverses the leads to the motor so that it turns in one direction during the wash and rinse cycle and in the opposite direction during the two spin cycles. Since the water pump is connected to the motor via a drive belt, it's the reversing direction of rotation of the pump that pumps the water out of the washer during the two spin cycles, but keeps it in the machine during the wash and rinse cycles.

    Probably one of the best sources of information from which to learn about electric motors is your own American military's training manuals. There is a company called "Intergrated Publishing" (w w w.tpub.com) that makes a business of selling these manuals to the general public. Since this information was compiled at the taxpayer's expense, it is owned by the American public. So, Integrated Publishing can't charge you for this information (since you own it already); it charges you for the service of loading that information onto a CD-ROM and mailing it to you.

    Integrated Publishing has all of the American military's training manuals online at:
    Repair and Maintenance Manuals - Integrated Publishing

    Probably the most popular training manuals are the Navy Electrical Engineering Training Series (or NEETS for short), and it can be found here:
    Neets - Naval Electrical Engineering Training Series
    Their electronics training manuals are also very well written and very popular.

    And, all I know about electric motors comes from the section on motors and generators, which can be found here:
    Neets Module 05-Introduction to Generators and Motors

    and the section on induction motors (which are the kinds of motors most commonly used in furnace blowers, circulating pumps, washers, dryers and fridges can be found here:
    CHAPTER 4 ALTERNATING CURRENT MOTORS
     
    Last edited: Feb 15, 2010
  16. Feb 15, 2010 #16

    Wuzzat?

    Wuzzat?

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    Pun intended?
     
  17. Feb 17, 2010 #17

    Nestor_Kelebay

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    Wuzzat:

    I don't want to disappoint, but there's no pun to be found in there.

    In a washing machine spin cycle, the wash tub ROTATES about it's axis.

    The Earth REVOLVES around the Sun and the Moon REVOLVES around the Earth.

    Two completely different words to describe two completely different motions, just as Noah Webster would have seen good sense in.

    Or am I not seeing the pun you're suggesting is there?
     
    Last edited: Feb 17, 2010
  18. Feb 17, 2010 #18

    Wuzzat?

    Wuzzat?

    Wuzzat?

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    I have adjusted my Pun Detection neural network to give fewer false alarms. :p
     
  19. Oct 30, 2012 #19

    leor05

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    Hi

    My furnace motor will not run and will just make a humming sound then will eventually shut off. This is when the belt is attached to the fan but if i disconnect the belt from the motor then the motor will turn fine. Seems like the motor cannot carry anymore the turn even if I also tried to help it turn...
     
  20. Oct 30, 2012 #20

    Wuzzat?

    Wuzzat?

    Wuzzat?

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    There's high resistance in the line that supplies the motor voltage?
     

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