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  1. #1
    Join Date
    Jul 2004
    Location
    Alabama
    Posts
    6
    I have several 30GT carrier chillers to maintain. Several of these chillers don’t have a low side suction pressure switch to stop the compressor on a loss of suction. They are instead equipped with a “Loss Of Charge” switch that is connected to the discharge. What I have found a problem with the TXV or solenoid valve will cause compressor burn out on these machines.

    Connecting the switch to the low pressure side will cause the compressor to trip during the initial 10 sec pump down cycle. We have confirmed through the provided documentation that the switch is supposed to be connected the high side of the compressor.

    I have not been able to locate a low pressure safety on any chiller of this series. I am planning on installing low pressure protection on these machines in the very near future.

    I would like to know if any one has seen a single module solution to resolve this. The switch will have to be disabled during the initial start up of the compressor and not cycle the compressor on a actual low suction situation.


  2. #2
    Join Date
    Aug 2003
    Posts
    1,311
    i don't remember everything about the 30gt. but i believe the level of charge (LPS) is not a physical point in the system, the level of charge is monitored via thermistor input to the unit controller.

  3. #3
    Join Date
    Jul 2004
    Location
    Alabama
    Posts
    6
    This i checked into and there is a safety that applies only to EXV units that will shut the compressor down on a high superheat if that condition exist for 5 minutes.

    I went to all our chillers of this type today and confirmed that they will not shut down loss of suction.

  4. #4
    Join Date
    Aug 2003
    Posts
    242
    Those machines don't require a low pressure switch. The saturated suction temperature thermistor will monitor suction temp and shut down the unit on low suction temp if low on charge. The micro will also monitor superheat and trip if needed. These units have been out for 20 years and not having a low pressure switch is not an issue.

  5. #5
    traneman is correct. the processor board will monitor all thermistors and if there is a problem will shutdown chiller. also you cannot just wire in a low pressure switch. these units will pump out on startup. which would trip low pressure switch. now you could use a bypass relay parrell to pressure switch, but your wasting your time the processor will take care of any problems.

    you need to go to carrier and get a service manual for your machine. youll have a tough time working on them without it.

    also you may want topurchase the flotronic monitor software so you can hook up your laptop to unit and view all the thermistor , water and refrigerant tempertures and pressures.

  6. #6
    Join Date
    Jul 2004
    Location
    Alabama
    Posts
    6
    I will check into it only one out of 8 or our TXV equipped machines have thermistors. I think it origonally had EXV's and some one decided to put TXV's in it.

  7. #7
    Join Date
    Aug 2003
    Posts
    1,311
    the txv installation makes sence although i don't know what it does to the exv logics. the early exv's had serious problems due to having only 750 steps in the mechanism, later they used 1000+ steps (i think 1400 steps) and they had better internals.

    airworx,
    depending upon which of the flowtronic sries he has he may or may not be able to use computer to check it out. flotonics one with comfortview will not work out. flotronics II is good for it.


  8. #8
    doonehill. not all models have thermistors and exv (flotronic)
    some models come with txvs.

  9. #9
    Join Date
    Aug 2003
    Posts
    242
    Airwox is correct. Not all models of the early 30GB / 30GT chillers had EXV's and thermistors.

  10. #10
    Don't try to outsmart the system software. The system will trip on high suction superheat long before it will trip on a ad on low pressure switch. If you are losing refrigerant
    check you quarter inch oil equalizer lines on the bottom of each compressor they leak all the time. You realy can't add on a low pressure switch

  11. #11
    Join Date
    Jul 2004
    Location
    Alabama
    Posts
    6
    We aren’t loosing charge we burnt out 3 different compressors this year because of solenoid valve failures. We haven’t been able to make a TXV controlled chiller shut down on superheat.

  12. #12
    i would check to see if the discharge gas hi temp switch is not stuck closed. also why is solenoids failing. are compressors pumping down and not shutting off. i would go to carrier and get a service manual for this machine. very difficult to work on if not experienced on flotronic equipment without manual.
    also check into flotronic monitor so you can hookup a laptop to machine you can tell a great deal more of whats going on.

    if you just can't figure out whats causing these problems you could install a lowpressure switch with a bypass time delay wired in parrallel to pressure switch but i would rather repair the problem instead of manifesting a solution.

  13. #13
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,700
    Is your oil pressure switch not catching it?

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