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  1. #1
    Join Date
    Jun 2019
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    Help with walk in freezer...low TD at evap coil/low subcooling/normal superheat

    ODA 88 deg. F.
    Freezer: -3 deg. C
    Box: 16'X8'X8'/concrete floor
    SH @ evap: 10 deg. F
    Ref: 404a
    ST @ odu: 2-3 deg.
    Suct. Line Temp @ evap: 12-13 deg. F
    all ubends frosting
    max box temp after 3 days -9 deg. C
    TD @ evap: 5-6 deg. F
    Light load...medical supplies
    Sat temp from gauges: 100 deg.
    LL temp at odu: 95 deg. F
    subcooling 5 deg. F
    condenser and fan coils have been cleaned
    sight glass clear
    head press: 245 PSI
    Suct. Press: 35 psi
    ODU: Heatcraft M0H015X63CFM
    IDU: Larkin LCA6110AB
    I'm trying to get -10 to -20 C
    TXV is hunting...not sure how I can have 10 deg. superheat when subcooling only 5 degrees. Any suggestions or ideas before I resort to drastic measures?

  2. #2
    Join Date
    Jan 2010
    Posts
    16,205
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    Don't worry about the sub cooling. It's got a receiver correct ?
    Did you try opening up the TEV valve to get your superheat down around 4f ?

  3. #3
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    7,548
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    Head is low for ambient and suction is too high.
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  4. #4
    Join Date
    Dec 2009
    Location
    maroon lazyboy
    Posts
    2,608
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    Please post all in Fahrenheit or at least all the same scale.

  5. #5
    Join Date
    Apr 2005
    Location
    Australia : Queensland
    Posts
    1,821
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    Lineset Length is ?
    Where is the condensing unit located ?

    How old is the Box & what construction is the floor ?
    Are you trying to cycle off on return air temperature or a room probe immersed in a glycol ?

    You have a SST of -16C

    Why do you want a box temp so wide of -10C to -20C.
    Minus 10 is achievable minus 20 maybe not depending on the above.
    The primary function of the design engineer is to make things difficult for the fabricator and impossible for the serviceman.

  6. #6
    Join Date
    Jun 2019
    Posts
    7
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    Thread Starter

    Receiver-yes. I was under the impression I needed 10 deg F SH at evap. TXV responds 4

    Quote Originally Posted by VTP99 View Post
    Don't worry about the sub cooling. It's got a receiver correct ?
    Did you try opening up the TEV valve to get your superheat down around 4f ?
    Receiver-yes. I was under the impression I needed 10 deg F SH at evap. TXV responds So should be able to achieve 4. Thx for your help

  7. #7
    Join Date
    Jun 2019
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    7
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    Thread Starter
    You think reducing my superheat by adjusting txv would help? Maybe try for a 270/20 split? Thx

  8. #8
    Join Date
    Jun 2019
    Posts
    7
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    Thread Starter
    50ft line set, condenser outside of structure on ground, 8 year old box, concrete floor, cycle off on return air, The lab technician says any temp between-10 and -20 C was acceptable. Im close but it took 3 days to get down to -9. Im worried it wont maintain with people going in and out. The equip is as old as the box. Was moved from another location.

  9. #9
    Join Date
    Apr 2005
    Location
    Australia : Queensland
    Posts
    1,821
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    As stated before by VTP99 SH is to high @10k. Get your Evap SH close to 5K & see how it performs.

    Have you done an effiency test on the compressor ? I would do this @ the same time you dial your SH back. As the box comes down to temp the SST should also drop back.

    What is your defrost control & is the coil clear of frost ? There is no ingress of outside air ?
    The primary function of the design engineer is to make things difficult for the fabricator and impossible for the serviceman.

  10. #10
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    22,272
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    Forget the SH @ the evaporator get it at 20 - 40F at the pump!

  11. #11
    Join Date
    Jan 2010
    Posts
    16,205
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    Quote Originally Posted by pecmsg View Post
    Forget the SH @ the evaporator get it at 20 - 40F at the pump!
    He's got a 50ft line he might be over 40f at the pump.
    What's your liquid line size ?

  12. #12
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    22,272
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    Quote Originally Posted by VTP99 View Post
    He's got a 50ft line he might be over 40f at the pump.
    What's your liquid line size ?
    I hope not!

  13. #13
    Join Date
    Jul 2000
    Location
    Guayaquil, EC
    Posts
    13,907
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    For a 8' x 16' x 8' 0 Deg F freezer I calculated the load would be around 11,500 Btuh.

    The MOH015X6 has a capacity of 5280 Btuh at -10 Deg SST with R404A and 90 Deg F ambient.

    You're way short on capacity as I see it, even for -10 Deg C.

    https://www.heatcraftrpd.com/PDF/LK%...D-HAD-.5-6.pdf

    https://boxload.tecumseh.com/EquipSelect.aspx

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