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  1. #1
    lennox rooftop gcs16 using the transformer to step down 575 power to 208/240 for blower fan moter and outdoor fan moter. I did not understand how the transfermor works.for example, the fan high black lead is 345 voltage. how much voltage I can measure after the transformer from the common lead ? usually if one power line is 120v,another is 120v, I mesure the voltage across two 120v power source is 208v. but here one line is 345v in the blower fan moter, another one from the transfermor. how does we get the 208/240

  2. #2
    Sounds like an autotransformer--try a search on the net for literature.

  3. #3
    I already read the diagram. today I did a service call, the fan moter is not working. I measured the resistance of the moter, it is too large. I did further to make sure the right power come to the moter. but I did not get 208v. I measured the common side is 256v( after the transformer step down). this cuased me to question how does the transformer works. you see, the fan moter one led connect to the 345 hot line. the fan common led connected to the transfermor. it is puzzled me and suspected the transformer is also not working properly

    [Edited by comfortable air on 01-05-2006 at 10:53 PM]

  4. #4
    Join Date
    Dec 2004
    460 V motors are commonly used for supply blower motor on 575 V lennox unit, are you sure the motor is 208/230?

  5. #5
    actually, I am not sure because I can not get the volatage of the blower moter. I just guess it is 208/230v. whatever, what is the principle of that transformer?

  6. #6
    Join Date
    Dec 2005
    Ive seen them on a 460 volt 3 phase unit it has a 460 volt primary and 230 volt secondary. Inducer is a 208-230 motor.
    Transformer is tapped of center of primary side giving 230 volts.

  7. #7
    your sayin the compressor is 575 and the incoming power is the same ... yet the indoor blower motor is less?!

    Never seen that.

  8. #8
    the indoor fan moter is one phase. . the compressor is three phase.

  9. #9
    Join Date
    Dec 2005
    Carrier and lennox both use single phase condenser fans indoor blower motor, and inducer motors on smaller equipment 3 phase.

  10. #10
    Join Date
    Aug 2000
    Austell, Ga.
    Autotransformers are basically transformers with "No" secondary...
    Just a Primary winding that is "Normally" tapped (Wired-Out) @ 20-40-60-80% of the Primary winding...
    The 40% tap on a 575V Autotransformer would give thou 230V.
    The downside of them is you would have full voltage in Ref. to ground....Not the 115v you might expect...
    Well over 350 jolts to burst ones puny Lil' heart should he/she have a lapse of thought and get a hold of one of the "230" volt leads...
    Makes the 460 volts seem lke a 9volt battery....
    Down heah' in the deeep' south we are blessed at all the old textile mills with 575 volts to contend with..
    Easy to see why people convert some of the 575v fan motors to 230v when you can buy 4 or 5 of the 230v motors for the price of the OEM 575v jobs...You also have to add the cost of either a transformer or an Autotransformer.
    Autotransformers "Much" cheaper....
    Autotransformers "Much" more dangerous....
    Autotransformers basically...Suck..
    Ain't "None" of us as smart as "All" of us..

  11. #11
    thank you. but I still not understand. yes, it don't have second winding. there are only three wire, two connect the hot line, one is out tap. If I connected the out tap to the ground , what reading can I get if it is 575v? the anther tap connected to the fan speed lead. If i measure voltage between the out tap lead and the another hot line lead, can I get 208v?

  12. #12
    come back to replace the old blower fan moter and found it is 460v one phase. checked the voltage from the transformer is 497v. it is in 10% difference. I am not sure wether I need replace the transfermor or not.

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