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  1. #1
    Join Date
    Jul 2008
    Posts
    414

    High amp draw on scroll compressor

    I just recentley replaced a scroll compressor (copeland zr18c something) on an Aaon rtu that had a grounded winding. The max operating amp draw is 15A per comp data tag. I draw consitentley 16-16.5 A across all 3 legs. Voltage to the compressor is good, I changed the contactor as well as filter drier, pressures are good around 68 psi back with 18* superheat (I know 18* SH is a little on the high side but there's a consitant load on the system as it serves a large pool area.). Fan cycling for head pressure control keeps it around 225 psi. I weighed in exactley the right charge, and used virgin 22. EVERY connection is tight and I even ohmed out the wires. I have no idea why I have such high amp draw. The second stg comp in the same unit draws around 10A as do both comps in the rtu right next to it serving the same area. I suppose I could just have a tight motor, dunno. Just looking for any input.

  2. #2
    Join Date
    Aug 2009
    Location
    Scranton Pa
    Posts
    24
    Tight motor, imperfection on the rotor resulting in higher friction. Who knows. Is it the digital modulating compressor?

  3. #3
    Join Date
    Jul 2008
    Posts
    414
    Quote Originally Posted by FlewtheCoop View Post
    Tight motor, imperfection on the rotor resulting in higher friction. Who knows. Is it the digital modulating compressor?
    No. Don't think ive seen that.

  4. #4
    Join Date
    Aug 2009
    Location
    Minnesota
    Posts
    14
    Few questions, Voltage is "good" what voltage is the unit, and what voltage do you actually have? Fan cycling on aaon RTU's run head pressure around 225-260 or so, but when the head pressure is in the 225 range are you still getting 16A? Is the high amp draw when both stages have been running together for a while or only when the #1 comp is running?

  5. #5
    Join Date
    Feb 2006
    Location
    SouthEastern Virginia
    Posts
    1,075
    Aaon probably got the tag wrong. I see it all the time cause I do their startups. Don't sweat it if the compressor is running good.
    It might get loud!

  6. #6
    Join Date
    Jul 2008
    Posts
    414
    Voltage is 460. Across each leg is around 468/465. Amp draw is high when both stages or just the first stage is running. The max operating rating is on the compressor itself and there are 3 identical withing the proximity and all draw around 10A under load. I think the motor might be tight.
    Last edited by dave1234; 08-21-2009 at 09:54 PM. Reason: Accidently sent before i was done- stupid laptop

  7. #7
    Join Date
    Jul 2009
    Location
    texas
    Posts
    49

    ohms

    get with copeland leftovers1tech support and ask what the windings should ohm to may have a winding trying to go to ground

  8. #8
    Join Date
    Nov 2001
    Location
    Seattle, WA
    Posts
    7,711
    When you picked up this three phase comperssor you should have received a start & test checking form. In this you are required to measure the differences in voltage to each leg. If out of balance by 5% or 10%, I don't remember which but I think it's 5%, then the motor will run too hot which will end up drawing higher then listed amps.

    Eventually the motor will overheat and cut out on thermals. Check with the manufacturer for these voltage difference figures and make sure the units power source is within those balance range or another compressor failure will take place.
    "The American Republic will endure until the day Congress discovers it can bribe the public with the public's own money.
    - Alexis de Toqueville, 1835

  9. #9
    Join Date
    Nov 2003
    Location
    Montreal, Qc.
    Posts
    761
    Being that the pressures are right it doesn't seem possible that it's an improper rotation issue but for those not used to working on 3 phase scroll compressors should read on.

    3 phase scroll compressors can only run in one direction.
    You can tell when it's running in the wrong direction by the metalic sound it makes and by the higher amp draw.
    Reverse the rotation by switching around any 2 wires and check amperage again.
    I bump start it for the first time and can tell right away from the sound if it's right.

  10. #10
    Join Date
    Aug 2009
    Location
    Minnesota
    Posts
    14
    Quote Originally Posted by thump_rrr View Post
    Being that the pressures are right it doesn't seem possible that it's an improper rotation issue but for those not used to working on 3 phase scroll compressors should read on.

    3 phase scroll compressors can only run in one direction.
    You can tell when it's running in the wrong direction by the metalic sound it makes and by the higher amp draw.
    Reverse the rotation by switching around any 2 wires and check amperage again.
    I bump start it for the first time and can tell right away from the sound if it's right.
    If it wasn't running the right way he would be telling us it fried after a few minutes and he didn't know why.

  11. #11
    Join Date
    Jul 2008
    Posts
    414
    Comp is diffenatley rotating the right way. Voltage available to the unit is balanced or else id have the same problem with the 2nd stg comp of the same unit, or at least i think i would.

  12. #12
    Join Date
    Jan 2009
    Location
    Paradise, NL, Canada
    Posts
    41
    since this is a replacement compressor the Rotation may be wrong even if the other compressor is correct.

  13. #13
    Join Date
    Aug 2009
    Location
    Minnesota
    Posts
    14
    Quote Originally Posted by BFG6868 View Post
    since this is a replacement compressor the Rotation may be wrong even if the other compressor is correct.
    He said his pressures were about right, if the rotation was wrong:

    1- The compressor most likely would be dead from running more than a short amount of time.

    2-The pressures would not be correct, back pressure would not fall into range with head pressure rising into range.

    3-The absurd noise would cause the tech to at least wonder and mention it in his post.

    I think that it is definately running the correct way. But--

    That said I would talk to copeland Tech line and see what they can offer.

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