Refer compressor tripping on motor overload. Please help!
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  1. #1

    Refer compressor tripping on motor overload. Please help!

    Hello, I am hoping some one on here might be able to give me some advice. I work offshore as the engineer on an anchor handling tug supply boat. Currently off of Nigeria. We have a PBUCH S.A. compressor/condensing unit for the walk in coolers and freezer. There are two identicle units side by side. Over night the unit on line had tripped off on motor overload. I reset the overload and restarted but the unit seems to be seized up and hums for a few seconds and then trips again. It had the correct oil level in the compressor and was working fine until then. I lined up the other unit and started it up and it ran well for a few days and then did the same thing. It tripped on motor overload and will not run. I swapped that compressor out with a spare that we had on board and this one runs for about twenty minutes but gets very hot, runs rough and makes a squeeky noise and eventually trips on motor overload.

    Does any one have any ideas? The compressor is a Bitzer semi hermetic reciprocating compressor using 404A. The condenser is cooled with a shell and tube sea water heat exchanger. The oil level in the compressor is correct, the condenser has good sea water flow, the charge seems correct. Is there more infor needed? Thanks for your time.

    Bob

  2. #2
    Join Date
    May 2009
    Location
    The Pas, Manitoba Canada
    Posts
    212
    Proper voltage?

  3. #3
    Join Date
    Jul 2012
    Location
    Western KY
    Posts
    1,221
    Need a little more info. SH, volts, amps, pressures, crank case temp. A lot of possible causes. When the 2nd unit came up and was running was it cooling? Is anything else on the boat acting strange, tripping breakers or browning out maybe?

  4. #4
    Join Date
    Aug 2012
    Posts
    2,515
    Clogged condensers or no water flow.
    Trying not to be a Hack.

  5. #5
    They run on 440V 3PH, 60HZ. The voltage and frequency are good. I'm not sure what the amperage is. I'll try to check. No other equipment on board is acting strange. The suction pressure while running is .4MPa (60psi) and the discharge pressure is 1.7MPa (255psi) and it is cooling the boxes but it trips off too quick to bring them down more than a few degrees. They're all at about 30 celcius right now. We haven't had a black out or brown out in a long time.

    When the second unit came on line after the original unit tripped off, it ran for several days and kept the freezer down to -20* C, cooler to 5*C. But now the new compressor won't run for more than 20 minutes or so.

    Thanks for the replies.

  6. #6
    Water flow seems good. there is a big temperature difference in refrigerant in and out of the condenser.

  7. #7
    Join Date
    Apr 2007
    Location
    Scottsdale,AZ
    Posts
    80
    Are you checking voltage at compressor?

  8. #8
    I just checked at the compressor. 430V and 14.5A per leg.

  9. #9
    Join Date
    Jul 2012
    Location
    Western KY
    Posts
    1,221
    Check SH at comp and evap. Is there a suction filter?

  10. #10
    Join Date
    Aug 2012
    Posts
    2,515
    What is the temp rise of the water thru the heat exchanger?
    Trying not to be a Hack.

  11. #11
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,248
    What is the Bitzer model number for these compressors? Is the internal overload tripping or do you have a starter with overload heaters which are tripping?

    Bitzer has a performance calculator where you can plug in the model number, supply voltage, suction & discharge pressures and it will tell you what the amp draw should be. You can download it and do it yourself, or we can run the numbers for you:

    http://www.bitzer.de/eng/products/prod/software/1

  12. #12
    Join Date
    Jul 2011
    Location
    Lehigh Valley, PA
    Posts
    427
    Check the overload relays on the motor starter. Are they sized correctly or possibly corroded? How bout the motor starter contactors? Look for corrosion there too.

  13. #13
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,248
    I'm curious as to how this system is set up. You say there are two compressors with one valved off as a standby...which I've seen before for marine applications like this...but are both the freezer and the cooler running on the same compressor, perhaps with an EPR valve on the cooler? I've seen that arrangement too.

    I ask because you stated your suction pressure was running at about 60 psig, and on R404A that would typically be high enough to overload a low temp compressor.

    Does this system have crankcase pressure regulator (CPR) for the compressor or possibly a pressure-limiting MOP type TXV on the freezer?

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