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  1. #40
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    The motor running backwards would not burn up the motor in an hour.

    If the black and white wires are connected to the correct voltage for the new motor - and the capacitor is correct for the motor - the motor would not burn up in one hour.

    Based on what little actual data we have here - I can't think of an option - other than incorrect voltage being applied to the installed motor - which Would burn up a motor in one hour.

    A hint might be had in the fact that a universal blower motor would not be very 'universal' if it had only a black and white wire for powering it. Couple that with the fact that the vast majority of condenser fan motors are single speed . . . . <g>

    PHM
    ------




    Quote Originally Posted by wxguo1 View Post
    The new motor RPM is 1037. I really don't know the original RPM and fan speed. It is a fairly old unit.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  2. #41
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    May 2019
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    Is this a gas furnace with the standard 120 VAC motor or heat pump air handler typically being 208/240 VAC? (some older heat pumps had a single speed for both heat and cooling)

  3. #42
    Join Date
    May 2014
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    Just go buy the OEM motor and cap and be done with it.
    I do a triple evac with nitro to remove non condensables.

  4. #43
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    Quote Originally Posted by wxguo1 View Post
    The new motor is universal one, only have four wires, two browns, a black and a white. Voltage is correct. Rotation, not sure, I used the one has 1037 RPM, not sure what the old one was. I thought this would be alright. Capacitor wise, I used 7.5uM. My senior tech told me usually it is okay to be within 5-7.5uF
    Caps are specific to the motor. It does not matter what the old motor had for a cap the new motor may need one a different size, and just because a certain size motor of one brand uses X that doesn't mean that every motor that size used the same size. I have seen blower motors use anything from none to 20 uf.

  5. #44
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    That's an excellent point.....the cap that should be used with any given motor is the cap that is listed on the motor's label.

    There is a methodology for determining the correct capacitor using equipment in an electronics lab.... but the easiest way in the field if you do not know the capacitor value is to try two or three reasonable capacitor sizes, and the one that produces the lowest current draw under identical conditions (same speed, blower door in place, etc) is the one that you should use.

    Most of the time if I cannot read the capacitor value on a motor which is already in service, I can go to a similar piece of equipment nearby on the same roof, and sometimes have better luck being able to read that label.
    [Avatar photo from a Florida training accident. Everyone walked away.]
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  6. #45
    Join Date
    Jun 2019
    Location
    Houston, TX
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    Thread Starter
    Quote Originally Posted by Poodle Head Mikey View Post
    The motor running backwards would not burn up the motor in an hour.

    If the black and white wires are connected to the correct voltage for the new motor - and the capacitor is correct for the motor - the motor would not burn up in one hour.

    Based on what little actual data we have here - I can't think of an option - other than incorrect voltage being applied to the installed motor - which Would burn up a motor in one hour.

    A hint might be had in the fact that a universal blower motor would not be very 'universal' if it had only a black and white wire for powering it. Couple that with the fact that the vast majority of condenser fan motors are single speed . . . . <g>

    PHM
    ------
    Hi, there, you're probably right on one of the two that burned in an hour. The power feed the blower motor is 240 volts. The other one uses 115 volts to power the motor, which shouldn't burn it in an hour as well. Anyway, I am going to take both down tomorrow, and ask the senior guys before order new ones. Thanks

  7. #46
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    Sep 2014
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    Charlotte NC 28213 USA
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    Quote Originally Posted by wxguo1 View Post
    I have two customers whom I replaced the blower motors for them. Interesting and frustrating, in both cases approximately two hours after I left, the motor stopped working again. When I tested the motors, the windings seem OK, but the motors are all very hot, not working anymore, even if directly connected to power line. capacitors are good. I used universal motors(two wires not including the capacitor wires) to replace the four wires motors. Anyone could point out what I did wrong? Thanks ahead!
    " I used universal motors(two wires not including the capacitor wires) to replace the four wires motors"
    What kind of universal motors you used ? Only 2 wires motor ? It seemed you had used the motors for condenser unit ? If so your universal motors are for 230VAC and it could be a problem if your use it on furnace 120VAC.
    I 've used a lot alot of universal motors to replace the OEM ones but I never seen a UNIVERSAL BLOWER MOTOR 120VAC or 240VAC that has only 4 wires.

  8. Likes Metalman0880 liked this post.
  9. #47
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    Aug 2002
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    Quote Originally Posted by wxguo1 View Post
    Hi, there, you're probably right on one of the two that burned in an hour. The power feed the blower motor is 240 volts. The other one uses 115 volts to power the motor, which shouldn't burn it in an hour as well. Anyway, I am going to take both down tomorrow, and ask the senior guys before order new ones. Thanks
    Again

    No voltage readings
    No Amp readings
    Wrong HP
    Unknown rotation


    Be careful, be very careful out there. You are not ready for service! If you screw up lives can and do get lost!

  10. #48
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    Quote Originally Posted by wxguo1 View Post
    Hi, there, you're probably right on one of the two that burned in an hour. The power feed the blower motor is 240 volts. The other one uses 115 volts to power the motor, which shouldn't burn it in an hour as well. Anyway, I am going to take both down tomorrow, and ask the senior guys before order new ones. Thanks
    I don't understand, you used the same motor on 2 units, 1-240V the other 120V? I thought you lost 2 motors in 1 unit! What were the motors rated at 240, 120, or 1 of each? Were these open/ventilated motors or totally enclosed? Were they rated for blowers or condenser fan?

  11. #49
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  12. #50
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    Quote Originally Posted by BNME8EZ View Post
    I don't understand, you used the same motor on 2 units, 1-240V the other 120V? I thought you lost 2 motors in 1 unit! What were the motors rated at 240, 120, or 1 of each? Were these open/ventilated motors or totally enclosed? Were they rated for blowers or condenser fan?


  13. #51
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    Mar 2018
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    Quote Originally Posted by BNME8EZ View Post
    Caps are specific to the motor. It does not matter what the old motor had for a cap the new motor may need one a different size, and just because a certain size motor of one brand uses X that doesn't mean that every motor that size used the same size. I have seen blower motors use anything from none to 20 uf.
    Or a Lennox blower motor with a 40uf.

  14. #52
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    Sep 2019
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    Read the schematic on the side of the motor on how to wire. A black and white sounds like a condenser fan motor tho. All blowers I've seen have at least 2 speeds, most 4.

  15. Likes CEAS-AC-TECH liked this post.
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