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  1. #1
    Join Date
    May 2004
    Location
    Austin, TX
    Posts
    1,733

    Semihermetic compressors.

    This is a loaded question, and am sure answer varies, but here goes....

    How long should a new Copeland Semihermetic compressor last in a
    refigeration system.

    I have two Heatcraft refigeration systems in a warehouse, one a 20 ton
    system and the other a 30 ton system. This warehouse not insulated
    that well, so systems run majority of time. There is actually a third
    system that is a 12 ton system, but not talking about this one now.

    The 20 ton system keeps room at 58 degrees, and 30 ton keeps room
    at 36 degrees. Both systems use R22. The 20 ton system compressor
    died last fall when system was 4 years 10 months old, had to replace
    compressor. When I drained the oil there were a lot of brass shavings
    in the oil, so bearings must have given out.

    Today the 30 ton compressor died, locked up and blew fuses. Had my
    helper go check the windings one shorted, one high ohms. These
    compressors are 3 ph 460 volt.

    Both of these units were working flawlessly, never had any problems,
    check them once a year, clean evap coils, check pressures, never any
    problems, the 30 ton runs 95% of the time, the 20 ton about 70% of
    the time.

    Is 5 years about how long units that run most of the time should last,
    or is this just a unusual event. I have had other semihermetics fail,
    but they had a reason to fail. These two times everything normal.

    The oil minders were working fine, and both units had phase protectors
    that worked. No reason for them to both fail, other that a critical part
    gave out. We know the 20 ton failed because of bearing failure, right
    now do not know why 30 ton failed yet, it was 109 degrees outside
    when unit died. Oil up to half way mark on sight glass, an oil is clear.

  2. #2
    Join Date
    Jun 2003
    Location
    Chicago, IL
    Posts
    4,458
    In my opinion they should last almost indefinitely. I have many customers with semis over 30 years old.

    When a compressor breaks its usually because something killed it.

  3. #3
    Join Date
    Dec 2011
    Location
    New Zealand
    Posts
    2,224
    I find semi's to be very reliable.
    Looking at the size it would seem these compressors, are lubricated by a positive pressure oil pump.
    So my gut feeling is that you have some shtye in the oil channels ways feeding the bearings. I presume you have a low oil pressure diff switch fitted, that works!
    Being R22 high discharge temps can be a problem (not normally at your stated room temps), but if you had high compressor suction superheat, then high discharge temps could cause so breakdown of the oil.
    Any discoloration of the comp heads?
    Does the system run for very long periods unloaded?

  4. #4
    Join Date
    May 2004
    Location
    Austin, TX
    Posts
    1,733
    These have positive pressure oil pumps. System does have a low oil
    pressure diff switch.

    The heads are not discolored.

    On the last unit that died, I pulled the oil pressure sensor, and the screen
    was clean.

    Compressors are rarely unloaded.

    I have seen many old semis, that is why these two have me stumped.
    When I open up this 30 ton compresser, hopefully I can find a reason
    for the early death.

  5. #5
    Join Date
    Apr 2012
    Location
    Paper Street Soap Company
    Posts
    2,304
    Usually flood back is the killer of a semi-hermetic. Washes out the rear bearing and causes enough play for the rotor to contact the stator.

    Either flood back or slugging on start up

    Ive seen a running 40 year old semi hermetic with perfect oil pressure.

  6. #6
    Join Date
    Jun 2010
    Location
    Miami
    Posts
    258
    How often do you test oil for acid and metal content? That and a log of megger readings might be worthwhile.

    I have a whole bunch on semi's from the 70's going strong. Most copeland but a few carlyle and bristols (I think).

    I agree with post on hot gas discharge temps and high suction superheat. High superheat can often add up to poor oil return and then possible oil slugging later on.

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