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Thread: wiring ac blower fan motor?

  1. #1
    epiguy is offline New Member
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    wiring ac blower fan motor?

    I need some help wiring a grangier fan motor in my American Standard Air Handler.

    The GE fan motor I removed had a set of three terminals for high, med and low speed and a set of black and yellow wires that went to the start cap. and of course the ground wire.

    The Grainger has black, red and blue wires for high, med and low. Purple for comon and two brown wires for the start cap.

    From the unit I have a red wire that originally went to the GE high, med or low terminals and a black wire that went to the start cap.

    its HOT!

    Thanks,
    epiguy

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    HayZee518's Avatar
    HayZee518 is offline Deity
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    ok, purple is ground or neutral. brown to the cap. rest are for the speeds. get ne a grainger stock no. I can tell you better if I had the info from grainger.

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    epiguy is offline New Member
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    The old GE fan motor is 3 speed single phase 230 volt. There were two wires coming out of the motor yellow and black and they went to the start cap. The red wire from the relay went to one of three terminals either high med or low.

    The new Grainger is #4M101. The motor does not have the same terminals and had to be hardwired. I wired the red wire from the relay to the high speed (black) wire on the motor. I put wire nuts on the other two medium and low speed wires. Then the two brown wires from the motor I wired to the cap. I ran the black wire from the unit to the same side of the cap as it was on the old cap. The purple common wire from the motor I tried with just a wire nut and also tried it connected to the left side of start cap.

    Everything works but the motor is turning very slow.

    Am I only getting 110 volts to this motor?

    Thanks!!

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    HayZee518's Avatar
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    I went to the grainger site and found the motor. they also had a pdf file so I looked at this also. the wires for a half horse 208-239 volt motor are - two brown [for the cap] a purple [one side of the line] a black, high speed - red, medium-lo speed, yellow - low speed. the three wires blk, red, yel go to your speed switch.

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    the start cap just connects to the brown wires. it is internally disconnected when the unit is running

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    Rather than try to guess what the problem is let us go back to the beginning and start over.

    First switch the breaker off and check for voltage at L1 & L2 on the unit. When you are sure there is no voltage we can precede with the motor change.

    The OEM (original equipment manufacturer) motor is a 3 speed motor that is user defined to operate as a single speed motor by selecting which internal tap the red wire was connected to.

    Check the data plate on that motor and it should list the RPM for each tap, H, M, L. It is vitally important that you determine what the original speed was because the load of a squirrel cage fan changes proportional to the RPM. If the fan is operated at a speed higher than specified it will cause an additional mechanical load on the new motor, which may put it above the HP rating of the motor. In that case the new motor would be in a constant overload condition and will run hot and fail prematurely. If the RPM is too low the load will be considerably less than the rated HP of the motor. The “Inductive Reactance” which is the AC electrical resistance of the motor windings primarily determines an electric motors AMP draw. When a motor is properly balanced to the load all the electrical energy entering the motor is converted to mechanical energy and taken out of the motor by the load. There is a law of physics that states that energy cannot be created nor destroyed but only changed in form. In the case of a motor the reactance of the winding determines how much energy the motor will draw but if the load is less than the amount of energy entering the motor the excess energy will be dissipated in the form of heat, which again will result in premature failure of the motor.

    When you determine the proper RPM you then check the data plate on the new motor to determine which winding will produce the same RPM. Typically blower motors operate at 1075RPM and most likely that will be the High speed for both motors.

    The industry standard color code is:
    Black …High Speed
    Blue…. Med Speed
    Red … Low Speed
    Brown.. Capacitor
    Brown with White stripe.. Capacitor Common (Connect to the identified connector on the capacitor.)
    White or yellow.. Line 2 or motor common

    Once you have determined the correct wire for the proper speed you will connect that wire to the Fan Relay output terminal. The other two speed wires are then capped off and not used.

    The two brown wires on your motor are connected to the run capacitor.

    You new motor has two more wires, a brown wire and a purple wire. Check the motor data plate carefully. Your motor is reversible. One of those two wires is common for clockwise rotation and the other is common for counter-clockwise rotation. When you determine which rotation you need you then connect that wire to L2 in the unit. The other rotation wire is capped and not used.

    (See attached illustrations.)
    Attached Images Attached Images  

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    clegg (03-13-2009)

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    granadaCoder is offline New Member
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    L1 << >> L2 for my application

    Quote Originally Posted by LazyPup View Post
    Rather than try to guess what the problem is let us go back to the beginning and start over.

    First switch the breaker off and check for voltage at L1 & L2 on the unit. When you are sure there is no voltage we can precede with the motor change.

    The OEM (original equipment manufacturer) motor is a 3 speed motor that is user defined to operate as a single speed motor by selecting which internal tap the red wire was connected to.

    Check the data plate on that motor and it should list the RPM for each tap, H, M, L. It is vitally important that you determine what the original speed was because the load of a squirrel cage fan changes proportional to the RPM. If the fan is operated at a speed higher than specified it will cause an additional mechanical load on the new motor, which may put it above the HP rating of the motor. In that case the new motor would be in a constant overload condition and will run hot and fail prematurely. If the RPM is too low the load will be considerably less than the rated HP of the motor. The “Inductive Reactance” which is the AC electrical resistance of the motor windings primarily determines an electric motors AMP draw. When a motor is properly balanced to the load all the electrical energy entering the motor is converted to mechanical energy and taken out of the motor by the load. There is a law of physics that states that energy cannot be created nor destroyed but only changed in form. In the case of a motor the reactance of the winding determines how much energy the motor will draw but if the load is less than the amount of energy entering the motor the excess energy will be dissipated in the form of heat, which again will result in premature failure of the motor.

    When you determine the proper RPM you then check the data plate on the new motor to determine which winding will produce the same RPM. Typically blower motors operate at 1075RPM and most likely that will be the High speed for both motors.

    The industry standard color code is:
    Black …High Speed
    Blue…. Med Speed
    Red … Low Speed
    Brown.. Capacitor
    Brown with White stripe.. Capacitor Common (Connect to the identified connector on the capacitor.)
    White or yellow.. Line 2 or motor common

    Once you have determined the correct wire for the proper speed you will connect that wire to the Fan Relay output terminal. The other two speed wires are then capped off and not used.

    The two brown wires on your motor are connected to the run capacitor.

    You new motor has two more wires, a brown wire and a purple wire. Check the motor data plate carefully. Your motor is reversible. One of those two wires is common for clockwise rotation and the other is common for counter-clockwise rotation. When you determine which rotation you need you then connect that wire to L2 in the unit. The other rotation wire is capped and not used.

    (See attached illustrations.)

    First, let me say thank you for this post. You saved the day. The original wiring had very little to do with what the final result (in my case) ended up being.

    Here was my situation:

    I have a Trane TWV736B140A0. Recently, the blower motor went out. When I pulled the blower motor, I found the motor model number to be: (GE) 5KCP39LGG451S or slightly less precise model number 5KCP39LG. (The G451S suffix was in bigger letters than the earlier numbers, fyi).


    The only difference I had was that the purple wire was labeled as "L1" on my wiring diagram. And the black/blue/red was labeled "L2".

    I wired them up as such in my application.

    On the source wires, I had a red and black wire. I think that is what is confusing for the newbie (aka, me in this case).
    When you wire 110, you have a black and white wire, and black goes on the gold terminal, and white goes on the silver terminal. On an outlet (3 prongs) black goes to the smaller vertical slot and white goes to the bigger vertical slot (and green/copper goes to the ground slot of course).

    Anyways, knowing which source wires to hook up to L1 or L2 on the motor is the small missing link for me and my newbie-ness.

    ........

    Regardless, I got it up and running, with this post and the diagram.

    Thanks.

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