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  1. #1
    Join Date
    Jun 2008
    Location
    Jacksonville, Florida area
    Posts
    59

    Fluctuating Suction Pressure - Air Cooled Chiller

    I have a 60 ton air cooled water chiller with 4) 15 ton scroll compressors. There are two circuits with two compressors in parallel on each circuit. One chilled water evaporator tube bundle with two circuits in it. The problem is in fluctuating suction pressures in circuit 1, with the drop low enough to trip the low pressure lockout switch. It runs for a day or so but the suction pressure goes from 58 to 48 in 60 second cycles. Circuit 2 runs pretty steady between 60 and 63 psig.

    The dryer has been replaced and the sight glass shows a dry system. Thought the TXV could be the cause and it has been replaced only to have the same issue. Water side is common to the other circuit which does not have this problem. Superheat running 17-18 degrees, subcooling running between 8 and 13 degrees. refrigerant was weighed in to factory nameplate but it looks like it could use more refrigerant based on the subcooling. Before the TXV was replaced tried adding more refrigerant than nameplate and it did raise the suction some but it still had the fluctuating situation. I am leary of overcharging by 15 or 20 pounds on a system that is supposed to have a 65 pound charge. Any thoughts?

  2. #2
    Join Date
    Feb 2010
    Location
    MEXICO
    Posts
    475
    which is the flow of water in the evaporator? the water filter is clean. TXV bulb is secured and the right distance

  3. #3
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
    Posts
    2,132
    Model and serial numbers would help...

  4. #4
    Join Date
    Dec 2009
    Posts
    171
    Quote Originally Posted by Nuclrchiller View Post
    Model and serial numbers would help...
    ^THIS. Does this circuit have hot gas bypass? Whats the ambient? Give us some details please.

  5. #5
    Join Date
    Oct 2001
    Posts
    6,966
    definitly the water vs the freon hitting the barrel after the TXV,is the oil still showing in all the compressors especially the problem circuit.how is the water temp coming into the barrel on that return lock out NO.2 and see how the suction on 1 handles the load.if your missing oi in both CKT-1 cppressor just below glass it might be in the evap...runn the head up locking out the cond.fans to run it just beow trip for an hour or so might flush the evap if the oil is coating the tubes on the CKT-1 side
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

  6. #6
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Thread relocated to the "Chillers open forum"

  7. #7
    Join Date
    Jul 2009
    Location
    In a mechanical room....
    Posts
    1,888
    Please provide some more info, sounds like the txv is searching....
    what application is it
    temps in out of evap,
    pressure drops refrigerant if u can and water across the barrel,
    Model and serial of unit would be great
    what's your discharge superheat
    hgb?
    What's your low pressure cutting out at?
    “It takes courage to grow up and turn out to be who you really are.”

    - E.E. Cummings

  8. #8
    Join Date
    Jun 2008
    Location
    Jacksonville, Florida area
    Posts
    59
    Water flow is actually a little high at about 113 gpm vs 86 design per the pump curve. No hot gas bypass. As for temps in and out of evap, same result with a full or part load, 60 return and 50 supply or 50 return and 46 supply. Cuts out at about 18-20 degrees (41-43 psig). Ambients are 85-90. It is a Trane model CGAFC604AAEA10000DE, I'd prefer not getting into serial numbers.

  9. #9
    Join Date
    Feb 2010
    Location
    MEXICO
    Posts
    475
    commonly the power element of the TXV is damaged. cutting low temperature is 22 psig may be damaged pressure sw

  10. #10
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
    Posts
    2,132
    What is the actual diagnostic as read on the control panel? Word for word, please.

  11. #11
    Join Date
    Jun 2008
    Location
    Jacksonville, Florida area
    Posts
    59
    Latest alarm in the active diagnostics said: Manual Reset Comp Protect LPC Open. When I look in the logs, the first one which I assume is the active one, says Comp Protect LPC Open Ckt 1, The log 2 says Low Press Control Open Ckt 1, oddly log 3 says Evap Solution Flow Proving Sw

  12. #12
    SFTB is offline Bad email address, please contact Admin to fix
    Join Date
    Sep 2011
    Posts
    18
    Is ckt 1 on the same side as entering and leaving water? Baffles could be eroded and water could short circuit away from ckt on piping side. I would think your superheat would be lower than 17-18.

  13. #13
    Join Date
    Jun 2008
    Location
    Jacksonville, Florida area
    Posts
    59
    Actually circuit 2 is closest to the water connections on the barrel.

    For further information, I did some more testing and found that if only one compressor is running the pressures are normal and the compressor cycles on and off. When both compressors are running the pressure drops to the point of cutting out on low pressure. It got me thinking that maybe the LSV wasn't opening all the way. Rebuilt the LSV with a new enclosing tube and piston with the same results.

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