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  1. #1
    Join Date
    Jan 2012
    Location
    Oregon
    Posts
    101

    TXV valve problems

    I'm working on a r498 system that has high superheat. I've tried adjusting the TXV valves but the slightest adjustment makes them hunt. Or do TXV valves normally fluctuate? I can adjust the TXV valve for 20 degrees superheat but then it fluctuates between 15 degrees to 25 degrees. Never stays at 20 degrees. Is this normal? I adjusted it back to the center of the adjustment which I was told that's factory adjustment. But now my superheat is too high. Any advice would be good. Thanks. I'm new so don't laugh too hard at my question. Rusty

  2. #2
    Join Date
    Jan 2012
    Location
    Oregon
    Posts
    101
    R408 system not a r498. Sorry. Stupid iPad.

  3. #3
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,574
    Certain types of valves tend to "hunt" as a fairly normal part of their operation.

    Superheat isn't always a nice, even constant figure.

  4. #4
    Join Date
    Sep 2012
    Location
    Central Florida
    Posts
    885
    I'm not a refrigeration guru but is your system at design temp?

  5. #5
    Join Date
    Jan 2012
    Location
    Oregon
    Posts
    101
    So should I adjust the valves to where they are staying between 15 and 25 degrees and not worry about it? I just know that high superheat is a reason for premature compressor burnout.

  6. #6
    Join Date
    Jul 2011
    Location
    Nanaimo,BC, Canada!
    Posts
    346
    When ever you adjust a TXV it will hunt.. It will take at least 1/2 an hour for it to maintain its maximum stable signal.. If you think about how a TXV works it'll all make sense...

  7. #7
    Join Date
    Apr 2010
    Location
    San Diego, CA
    Posts
    204
    Hunting isn't a big deal. just make sure your discharge temp stays below 225 and your suction superheat at the compressor isn't below 20. these superheat numbers you're posting, are they at the evap or at the compressor?

  8. #8
    Join Date
    Jan 2012
    Location
    Oregon
    Posts
    101
    Yeah at the compressor. The superheat goes below 20 and goes above 20. 15 to 25

  9. #9
    Join Date
    Jun 2013
    Location
    Montana
    Posts
    73
    I might be naive but why adjust the superheat to the compressor? I thought you adjusted the superheat to outlet of the evap. If you have to much superheat back to the compressor couldn't that be caused also by a lack of insulation or going through hot zones? I do understand that you want a maximum amount of superheat to compressor for cooling the compressor and I would have to consult the manufacturer for that info.

    Also, I don't believe you can truely check superheat until the box/case has reached temp.

  10. #10
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,039
    Could be a sign valve is too big for application.

  11. #11
    Join Date
    Mar 2013
    Location
    swan valley idaho
    Posts
    727
    I would say check at box temp, shoot for 20-35 at
    Compressor and u will be good

  12. #12
    Join Date
    Jan 2012
    Location
    Oregon
    Posts
    101
    The box was at temp. I'm checking superheat at the compressor because I have a sman3 fieldpiece. It makes it easier because my digital gauge calculates superheat. Is it ok for the superheat to drop below 20 degrees as long as it doesn't stay below? Like I said the valves are fluctuating. Just wanting to make sure I protect the compressor.

  13. #13
    Join Date
    Jun 2013
    Location
    Montana
    Posts
    73
    So this is a multi case system?
    What is the compressor make and model?

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