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  1. #1
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    Aug 2002
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    Confused Liebert XDC Chiller Pump "Loss of Flow" Issues

    How many people are having flow loss issues with the Liebert XDC Chillers that use R-407C to cool the pumped R-134a? Also, is there anyone who has NEVER had this occur?

    We've determined multiple times that when an additional compressor stages on, the chilled R-134a pressure drops so fast that it loses subcooling at the pump inlet and flashes, even with a vessel half filled with liquid a few feet above the pumps. This loss of subcooling (flashing) causes the differential pressure switch to sense loss of flow. When this occurs and nobody is around, the server room temp gets out of control. When a technician is there, the SMA-12 test instrument is used to take control of the hot gas valves (Sporlan SDR valves) to prevent abrupt changes in pressure after an additional compressor stages on. It is a slow tedious process to keep the chiller running, by only moving the SDR valve for 1 to 4 seconds at a time, about once every minute or so. If the change happens too quickly, you lose flow and the compressors shut off, then you start all over again.

    The plate & frame heat exchanger is so efficient that it makes the R-134a flow become very sensitive to changes in the R-407c temperature changes.

    Does anyone have any suggestions as to the root cause of the problem?

    Has anyone come up with a solution to this problem?

    We have the XDC 160 (46 ton) chiller with 7 overhead XDO cooling coils. We have 2 bypass flow regulators (Griswold valves) and have tried all of the different combinations of closing the ball valves at one or both or neither bypass regulators. We don't have a pump curve or any information to verify the actual gpm of flow, but we're told that our flow is good because we have about 35 psig increase through the pump.
    I'm still learning this trade.

  2. #2
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    Apr 2006
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    i know this an old tbread but, did you ever resolve this issue ?

  3. #3
    Join Date
    Aug 2002
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    Thread Starter

    Confused Issue Resolved?

    Quote Originally Posted by coolerinfrederick View Post
    i know this an old tbread but, did you ever resolve this issue ?
    I'll get in touch with my former co-worker (I'm now retired) who was much more involved in this project than I was and possibly send you an e-mail message with more info. But, for a quick answer, the issue was resolved by removing the compressorized chiller from the server room and replacing it with a system using the plant chilled water to cool the R-134a that circulates to the overhead units.

    All of our very knowledgeable & experienced 'super techs' and some of the manufacturer's technicians and representatives and engineers could not determine any other way to resolve the problem, after many, many months of trying.

    So, my user name could be considered misleading, since just 5 years after posting the original post, I'm retired. I retired with 45 years of hands on experience in the field, but continued learning the trade, often feeling like an apprentice, my entire career, even while training new union apprentices.

    All I can say, in all sincerity is, "Good luck; and I feel sorry for you and the owner and users of the equipment."
    I'm still learning this trade.

  4. Likes mccann liked this post
  5. #4
    Join Date
    Apr 2006
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    well at least they were willing to dump the xdc's, im always learning myself with 17 yrs. experience, heck i just started working on pool equipment which is very unique, some units can have water cooled condensers to heat the pool water, a remote air cooled condenser, a reheat coil and even a hw coil in the rtu, obviously control strategies are very different as well, not only that, every manufacturer has their own controllers and logic

  6. Likes GoCougs liked this post
  7. #5
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    Jun 2012
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    Did you guys ever have Liebert come out and look? I know load and piping are very critical on these units. I have 4 at one site and never had this problem. Did anyone try to adjust or change the pressure switches? Was it only one of the pumps that did this or both? You had to be losing the liquid seal at the pump.

    I know this was a while ago so if you do not remember I would understand.

  8. #6
    Join Date
    Jul 2009
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    Had many of them. Only issues i had was when the unit was off for awhile and came back on. Sounds more of a capacity issue. Not allowed to have any less than 30-40% capacity or they run like ****.

    These units really love heat and work best hot.

    I did have 3 or 4 of these snap the pressure switch cap tubes and loose most the gas.

    Each time, i found a stuck open HGBP mod valve and 1 bank of compressors that had 1 grounded and 1 locked up.

    I swear the way the hgbp is piped, wouldn't allow oil to lube the rod and seat which would bind up.


    Sent from my iPhone using Tapatalk

  9. #7
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    Apr 2006
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    yeah thats what im hearing, low capacity can be a big issue and making sure the middle sight glass on the receiver is up halfway, but that kinda goes without saying

  10. #8
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    Jun 2012
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    Quote Originally Posted by gravity View Post
    Had many of them. Only issues i had was when the unit was off for awhile and came back on. Sounds more of a capacity issue. Not allowed to have any less than 30-40% capacity or they run like ****.

    These units really love heat and work best hot.

    I did have 3 or 4 of these snap the pressure switch cap tubes and loose most the gas.

    Each time, i found a stuck open HGBP mod valve and 1 bank of compressors that had 1 grounded and 1 locked up.

    I swear the way the hgbp is piped, wouldn't allow oil to lube the rod and seat which would bind up.


    Sent from my iPhone using Tapatalk
    I have had the same damn issues with the hot gas bypass valves. Replace then ALL the time. Them or the damn temp control boards for them. I think the stepper motor takes a dump then burns up the board. I am with you. Oil must not be getting to the inside of the valve. I don't think they should be piped like they are. I always wanted to repipe them so the motor was on top.

    When I first started working on these units and had problems with the valves a guy from Liebert just told me to replace all the boards and the valves because they do not know how to troubleshoot them. I did my own research and testing to learn how to troubleshoot them. I was surprised to see that it was Sporlans valve and Sporlan themselves had info on the valve and temperature control board but the people at Liebert had no idea!

  11. #9
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    Jul 2009
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    Columbia, MD
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    Yea. They are easy to work on. Nothing complicated. U can use a signal generator or buy their special tool


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