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  1. #1
    Join Date
    Jan 2008
    Location
    Las Vegas
    Posts
    18

    Question Ohm reading on scroll compressor

    Hey guys, working on a 5 ton York split system straight cool at a fire station. Single phase, 208/230 volt w/ danfoss scroll. Real quick history on the unit, two weeks ago construction supervisor noticed leak in condensing coil, ordered part and sent me to install. I put it in, leak checked, pulled vacuum, dropped in factory charge (starting point for my charge,) now compressor wont start. I have voltage, cap is good (though it's a 50mfd 370, and york dealer told me should be 60-70) Now my question, when i ohm out the windings they are closed and not grounded, but the ohms for all- common to start, start to run, and run to common are all 1.7 ohms. I know its bad but why, whats the technical term, also was it due to the fact theres no low pressure switch and the compressor ran w/ out refrigerant? thanks for the help

  2. #2
    Join Date
    Oct 2006
    Location
    Emerald Coast, FL 30.1N 85.8W
    Posts
    681
    Scroll windings will generally be lower than recips at the same tonnage.

    I did some winding checks on 4 & 5 ton scrolls today & got the following ohm readings:

    C-R 0.6
    C-S 0.8
    R-S 1.3

    The R-S on single phase should be the sum of the other 2 -- 3 phase motors have the same resistances on the windings (usually 3 phase windings measure less than 1 ohm).

    After you measure resistance at the terminals, it's helpful to reconnect the wires and measure resistance at the contactor & caps to see whether you have bad wires or loose connections -- you should have similar resistances.




    Quote Originally Posted by sncityA/C View Post
    Hey guys, working on a 5 ton York split system straight cool at a fire station. Single phase, 208/230 volt w/ danfoss scroll. Real quick history on the unit, two weeks ago construction supervisor noticed leak in condensing coil, ordered part and sent me to install. I put it in, leak checked, pulled vacuum, dropped in factory charge (starting point for my charge,) now compressor wont start. I have voltage, cap is good (though it's a 50mfd 370, and york dealer told me should be 60-70) Now my question, when i ohm out the windings they are closed and not grounded, but the ohms for all- common to start, start to run, and run to common are all 1.7 ohms. I know its bad but why, whats the technical term, also was it due to the fact theres no low pressure switch and the compressor ran w/ out refrigerant? thanks for the help

  3. #3
    Join Date
    Jan 2008
    Location
    Las Vegas
    Posts
    18
    [QUOTE=emcoasthvacr;1943653]Scroll windings will generally be lower than recips at the same tonnage.

    I did some winding checks on 4 & 5 ton scrolls today & got the following ohm readings:

    C-R 0.6
    C-S 0.8
    R-S 1.3

    This is what i generally see also, but for this one to have identical ohm readings between c-s, r-s, c-r is what threw me for a loop Have you seen identical ohm readings between windings on compressors before? if so, it's replacement time, right? Also good point on checking my wires going to compressor, will do that tomorrow. thanks for the help

  4. #4
    Join Date
    Apr 2005
    Location
    Boulder,CO.
    Posts
    559
    Has this unit ever ran or is it brand new?

  5. #5
    Join Date
    Jan 2008
    Location
    Las Vegas
    Posts
    18
    Unit is brand new. I personally never saw it run, but a tech did start up over a month ago and noted no problems.

  6. #6
    Join Date
    Jun 2006
    Location
    Midwest
    Posts
    284
    The compressor sounds lika a wannabe 3 phase . Perhaps it's one of the new hybrid compressors that runs on single or 3 phase power
    It's All Good!!!

  7. #7
    Join Date
    Mar 2006
    Location
    cincinnati, ohio
    Posts
    258

    Cool

    What is your amp draw?
    Knowledge comes with experience

  8. #8
    Join Date
    Nov 2005
    Location
    Shreveport, Louisiana
    Posts
    2,338
    Winding to winding short.
    UA Local 141

  9. #9
    Join Date
    Apr 2005
    Location
    Boulder,CO.
    Posts
    559
    I'd question the startup tech I think jimbob is right unit has the wrong comp. from the factory.

  10. #10
    Join Date
    Jan 2008
    Location
    Las Vegas
    Posts
    18
    Quote Originally Posted by controldude View Post
    I'd question the startup tech I think jimbob is right unit has the wrong comp. from the factory.
    I dont doubt it. After all the dual cap mfd rating for compressor was 20 mfd off. It was a 50/5 370v, when i called york they said with model # on unit it should be a 60- 70mfd for compressor and 5mfd was right for the fan motor. the three phase compressor being in this single phase unit would explain ohm reading...right?

  11. #11
    Join Date
    Jan 2008
    Location
    Las Vegas
    Posts
    18
    Quote Originally Posted by berg2666 View Post
    Winding to winding short.
    This was what a friend told me on the phone, an "internal short to power," but he didn't sount too sure.

  12. #12
    Join Date
    Oct 2006
    Location
    Emerald Coast, FL 30.1N 85.8W
    Posts
    681

    winding to winding shorts will measure less than 1 ohm

    on single phase comps -- you have to make sure you have a good connection when taking low ohm readings because they'll fluctuate.

    I constantly have to recheck my techs on comp diagnosis -- I don't want to look like a beavis to the manufacturers -- kinda annoying since I'm a licensed Professional Engineer and it takes away from my engineering responsibilities.

    Make calls to tech support -- they can walk you through while out in the field.

    On the Trane 4 ton recip, I got

    C-R .8
    C-S 1.7
    R-S 2.5

    which is lower than the scroll, but normal to Trane specs.

    Quote Originally Posted by sncityA/C View Post
    This was what a friend told me on the phone, an "internal short to power," but he didn't sount too sure.

  13. #13
    Join Date
    Jun 2005
    Location
    Las Vegas NV
    Posts
    1,152
    sncityA/C

    A model number would be helpful.

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