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  1. #14
    Join Date
    Jan 2012
    Location
    Oregon
    Posts
    101
    Yes this is a multiple case unit. 3 TXV valves, 6 evaporators, it's a copeland compressor. I believe it's a 5 horse. It's a big compressor and a big system.

  2. #15
    Join Date
    Apr 2010
    Location
    San Diego, CA
    Posts
    228
    Quote Originally Posted by bigbucks View Post
    Yes this is a multiple case unit. 3 TXV valves, 6 evaporators, it's a copeland compressor. I believe it's a 5 horse. It's a big compressor and a big system.
    You really need to be setting those valves based on evaporator superheat. The case manufacturer has spec'd out a superheat setting, and you need to try to get as close as possible to that, THEN check what it is at the compressor. You'll be going around in circles for quite a while trying to set superheat at the compressor with multiple valves.

  3. #16
    Join Date
    Jun 2013
    Location
    Montana
    Posts
    74
    Quote Originally Posted by cmclifton View Post
    You really need to be setting those valves based on evaporator superheat. The case manufacturer has spec'd out a superheat setting, and you need to try to get as close as possible to that, THEN check what it is at the compressor. You'll be going around in circles for quite a while trying to set superheat at the compressor with multiple valves.
    Ditto. if you have been tweeking on all of them I would start over with 3 turns out from all the way in and let system stabilize. What kinda of system? Open face, close door, walk-in? If you have open face display cases you can watch the discharge air on all you cases and see if they are metering the same ( not 100% acurate but can get you going in the right direction.)

  4. #17
    Join Date
    Jun 2013
    Location
    Montana
    Posts
    74
    Also on open face, make sure honeycombs are clean. Of cousre all fans working as well. What temp, medium or low?

  5. #18
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,957
    Quote Originally Posted by cmclifton View Post
    You really need to be setting those valves based on evaporator superheat. The case manufacturer has spec'd out a superheat setting, and you need to try to get as close as possible to that, THEN check what it is at the compressor. You'll be going around in circles for quite a while trying to set superheat at the compressor with multiple valves.
    ^THIS^

    Don't mess with trying to "set" superheat at the pump.

    Set it at the evaps and check it at the compressor as a verification.

  6. #19
    Join Date
    Sep 2002
    Location
    Virginia
    Posts
    3,335
    Quote Originally Posted by bigbucks View Post
    Yes this is a multiple case unit. 3 TXV valves, 6 evaporators, it's a copeland compressor. I believe it's a 5 horse. It's a big compressor and a big system.
    when they are all at temp with low load , they can hunt a little , no biggie

  7. #20
    Join Date
    Jan 2012
    Location
    Oregon
    Posts
    101
    Ok I will check the superheat at the Evaps. It's a low temp reachin. It's an old Tyler which they aren't around anymore. This system has never been fixed right so I'm guessing the superheat has never been right. When I started working on it the superheat was measuring 50 degrees at the compressor. Which is way to high

  8. #21
    Join Date
    Apr 2010
    Location
    San Diego, CA
    Posts
    228
    Quote Originally Posted by bigbucks View Post
    Ok I will check the superheat at the Evaps. It's a low temp reachin. It's an old Tyler which they aren't around anymore. This system has never been fixed right so I'm guessing the superheat has never been right. When I started working on it the superheat was measuring 50 degrees at the compressor. Which is way to high
    Not necessarily. Discharge temp determines whether or not the superheat at the compressor is too high. If it stays below 225 at all times, then it's ok.

    I'm currently looking at a Copeland performance sheet for a 3DSDF46KE compressor. It's showing performance with a 65 degree return gas temperature and shows performance all the way down to a -40 degree SSP. That's a whole lot more than 50 degrees of SH. Discharge temp is what matters, because that's how you know if the oil is burning in the cylinders. Suction superheat tells you if you're going to flood the pump. Discharge temperature tells you if you're going to burn the pump.

  9. #22
    Join Date
    Jan 2012
    Location
    Oregon
    Posts
    101
    I've been watching the superheat at the compressor. I was told that high superheat is the main cause for compressor burn out.

  10. #23
    Join Date
    Apr 2010
    Location
    San Diego, CA
    Posts
    228
    Quote Originally Posted by bigbucks View Post
    I've been watching the superheat at the compressor. I was told that high superheat is the main cause for compressor burn out.
    It's definitely a cause for compressor burnout. I'm pointing out that discharge temperature is the way to tell the whole story. If your superheat is too high, your discharge temp will be too high, and that's how you know your superheat is too high.

  11. #24
    Join Date
    Oct 2009
    Location
    Atlanta,Ga.
    Posts
    198
    All txv hunt a little,that shows it is opening and closing.box or space should be close to operating temp for final adjustment.If you want 10 degrees superheat,It may open and go to 6 degrees,then close and go up to 12,but the average would be 8-10.A txv is always opening and closing.If your hunting is too wide,you may have too big of a valve.Like a 14000 Btu coil,should have a 1 ton valve,not a 1.5 ton valve.the 1.5 ton will work,but not as well.you will get wider hunting.as the valve can not balance as well,being slightly oversized.The only vaves that i have seen stay almost exactlt set to maintain an exact superheat setting,are electronic tev valves.Such as on a Beacon system.

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