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  1. #1
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212

    What's wrong with this motor?

    Today I had a blower motor that wouldn't run.
    In the past, I've pretty much checked for 230V
    (or 115V, but this was a package), and tested
    the capacitance on the run cap, and then
    called it bad. Today, I did all that.

    But because it has been slow and I've
    been working at refining my HVAC tech approach,
    trying not to be so dumb about things,
    I went ahead and checked resistance between
    the three motor leads and to ground.

    Resistances were basically sound--something
    like 23, 43, and 66 ohms. Open to ground on
    all three.

    But when I applied power, the motor moaned
    and was locked--I couldn't spin the blower
    wheel with my screwdriver in either direction.
    With power not applied, the motor would turn but
    with some--but not a lot of--resistance.

    I'm sure the bearings aren't the best, but
    I would think the thing would spin a bit or
    at least until it warmed up. No. Are motors
    REALLY weak starting from a dead stop?
    Is that the problem here?

    This is disturbing me.
    Thank you for any enlightenment.

  2. #2
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,311
    Check for lateral bearing play: try for side to side motion at the shaft and you will feel your problem. When a motor starts the stator tries to pull the rotor into it. The bearings prevent this from happening. When the bearing wear is excessive enough that the two can meet you now have the equivalent of an expensive drum brake.

    For fun you can spin the blower when it's off, then apply power and watch it screech to a halt. Always feel free to tear into broken parts so you can see how they used to work, and why they failed.

  3. #3
    Join Date
    Feb 2011
    Location
    Cloverdale,Ca
    Posts
    299
    Did you check the Amp draw? LRA just for kicks? Did you try it on different speed? Many ways to experiment when you have a few minuites to slow down instead of hopping from call to call.
    Living the dream !!

  4. #4
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212
    Quote Originally Posted by Makinhole View Post
    Did you check the Amp draw? LRA just for kicks? Did you try it on different speed? Many ways to experiment when you have a few minuites to slow down instead of hopping from call to call.
    I did the amp draw. 3.0 Amps. Only three wires on this motor. Speed is selected by
    attaching black to one of several terminals on motor. I didn't pull the motor to check
    LRA and the label was messed up below the model number area. The blower
    motor had a built-in (on?) mount and I didn't want to monkey with a
    new mount, so I just ordered the factory motor, whatever it is.
    Didn't try different speeds. I got another call so I ran out of time
    as I was removing the blower assembly. It was only then that I noticed the mount.
    Duh. Next time, I will check that sooner.
    (Please don't ask for model/serial!! Notes at work. I know--not good when asking for
    forum help. This wasn't bugging me so much until I came home. But it was
    a Carrier heat pump, 1996, I believe. Looked older. Things were laid out
    poorly. Run cap difficult to access--could measure capacitance easily enough,
    but I also checked specification on label and had to loosen top of unit and
    lift it a few inches to remove cap. Blower assembly had five screws holding it in. Rod
    going across top of chassis opening very close to blower assembly. Contained
    thermostat wires--wasn't sure if that was done by the installer or the factory.
    Odd. I don't remember any part of the model number.)

  5. #5
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212
    I like the lateral play idea as I already know the bearings
    are not great. I can't say I really tried to wiggle it.

    The new motor is due from the factory next week so I will
    check it more thoroughly then.

    Thank you all.

  6. #6
    Join Date
    Feb 2013
    Location
    Lamar, SC
    Posts
    434
    This reminds me of a similar situation I was in. I got a call to replace a IFC on a Reznor commercial furnace for a church. The senior technician for our company (who had just retired) went there first and diagnosed the board bad. Since I dont like going behind someone else and just taking there word, I went ahead and checked out the other components myself, looking for shorts or anything else that could explain why the board went bad and found nothing. The inducer motor was a 120v unit, read 88 ohms and was not shorted to ground and spun freely. The old board was obselete and the new one included a retrofit kit that basically required rewiring most of the furnace controls and safeties. After almost an hour of fussing with all the wiring on the new board and double then triple checking my work, I applied power. As soon as the stat called for heat I heard a loud pop and the new board was done. Feeling sick I checked everything again, all wires went to right place, no shorts, no shorts to ground, and the motor still read 88 ohms and no short to ground. (the motor was two wire BTW) Just out of curiosity, I straight wired the motor to line voltage and turned the power back on and the motor made a pop. I checked the ohms on it again and this time it read open. I called the office and explained what happened, the owner called the other tech and he backed me up, said he checked the motor out also and it seemed fine and we ordered another board and inducer. The tech support guy said he had never heard of a motor killing a board before in his 20 years with the company. Replaced the motor and dropped in a second new board and the unit worked fine. What was wrong with this motor? ever seen it before? I havent run into the same problem again. BTW, I always check the inducer by straight wiring to line voltage on all bad IFCs now.

  7. #7
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212
    Do you know if the new motor measured 88 ohms?
    Was it shaded pole or PSC?
    (Why does it seem many (?) package units use PSC
    and split systems almost always seem to use
    shaded-pole?)

    My first guess would be that the bad one possibly
    had shorted windings.

  8. #8
    Join Date
    Feb 2013
    Location
    Lamar, SC
    Posts
    434
    Quote Originally Posted by georgelass View Post
    Do you know if the new motor measured 88 ohms?
    Was it shaded pole or PSC?
    (Why does it seem many (?) package units use PSC
    and split systems almost always seem to use
    shaded-pole?)

    My first guess would be that the bad one possibly
    had shorted windings.
    Shaded pole and and yes the new motor had the same resistance. It definitely had some kind of short but it just seems odd they didn't read short on either of two meters and then shorted when power was applied.
    Last edited by jmsmars1; 03-16-2013 at 04:09 AM. Reason: additional info

  9. #9
    Join Date
    Oct 2010
    Location
    Baton Rouge, LA
    Posts
    1,083
    Was this a single phase motor or a 3 phase motor? I'm guessing single just want to make sure.
    If you're too "open" minded, your brains will fall out.
    Artificial intelligence is no match for natural stupidity.

  10. #10
    Join Date
    May 2011
    Location
    Ripley, WV
    Posts
    1,132
    I agree with the statement about the bearings being the issue here. I believe what is happening is this: there may be excessive in and out play in the bearings and what this does is allow the rotor to get out of its proper position and instead of the poles inside the motor being of the same polarity and repealing one another to make the rotor spin, they are getting into a position where they are of different polarity and attracting to each other which is why when powered the motor is locked. My only bit of information to back this up came from working with condenser motors doing the same thing. What I observed was when the shaft was pointing down it's locked, if I pull the top and set it shaft up it allows it to get back into a more proper position and if powered it would start and run. As a note I want to point out that I have NO hard scientific evidence to necessarily back up what I believe, this is just some observations from the field that I gathered doing like Makinhole said having a few extra minutes instead of call hopping. BTW some of you other guys posting if you think I'm full of it please share you thoughts as well, because I definitely don't know it all and would like to hear other theories to better advance my own understanding.

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,808
    Quote Originally Posted by jmsmars1 View Post
    Shaded pole and and yes the new motor had the same resistance. It definitely had some kind of short but it just seems odd they didn't read short on either of two meters and then shorted when power was applied.
    If you had a capacitor to test, it wasn't a shaded pole motor.

    Start winding is shunted to itself.
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  12. #12
    Join Date
    Feb 2013
    Location
    Lamar, SC
    Posts
    434
    Quote Originally Posted by beenthere View Post
    If you had a capacitor to test, it wasn't a shaded pole motor.

    Start winding is shunted to itself.
    No capacitor and no start winding. I remember the intake air pipe was having some condensation issues allowing water to get back to the burners so they were rusty and I had to clean out the little holes on the side that let flame jump from one to the other because ignition was on one end and flame rod was on the other. (the first half of the burners would light then the unit would shut off because the flame didnt make it to the other side) I wonder if moisture could have been an issue but dont see how it could have got from the air intake to the inducer.

  13. #13
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212
    OP, here.
    I went back and installed the new factory motor this morning.

    After I removed the motor from the blower assembly, I noted that
    the bearings were rather rough AND the thing had maybe a quarter
    inch or more of axial freeplay--that is, along the shaft.

    New motor works much better. Resistances were very close, all about
    1 or 2 ohms less.

    THank you all.

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