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  1. #1
    Join Date
    Jul 2007
    Location
    Chicagoland
    Posts
    474

    Copeland scroll with "discharge temp control"

    I'm taking on a seasonal client with two fry kitchens at one three year old property. Both kitchens have generous walk in cold storage, all the boxes are cooling fine. The condensing units for the two (same size) freezers are different, in that one has a Copeland scroll with, what the supply house says is a "discharge temp control valve". Having never encountered this control before, I hope someone who has might enlighten me, or lead me to enlightenment on how to tell when this control is working correctly and when it is not.
    Thanks

  2. #2
    Join Date
    Apr 2005
    Location
    Central California
    Posts
    186
    Yes the "dtc" injects liquid into the compressor to keep discharge temps within range. It has a sensing element that is in the dome of the compressor. You find these on a lot of "zf" compressors. It tries to maintain a 195 degree temperature +\- 5 degrees. This keeps from burning up the top bearing and also keep the oil intact.

    The lower the coil temp the lower the suction pressure the higher the compression ratio which equals heat. Need the liquid to offset the heat. They are pretty much bullet proof imho.
    Only Chuck Norris can slam a revolving door

  3. #3
    Join Date
    Jul 2007
    Location
    Chicagoland
    Posts
    474
    Quote Originally Posted by mr kev View Post
    They are pretty much bullet proof imho.
    So in your opinion unless discharge temp is excessive, I should trust that its working correctly?
    The reason I ask is that on one day in particular I observed the DTC metering constantly, leading to an ice coating and, more concerning, after pump down it bled by enough to bring the compressor back on in short bursts 1 to 3 times after each cycle. On two successive visits neither symptom was observed.

  4. #4
    Join Date
    Apr 2005
    Location
    Central California
    Posts
    186
    I found this link to a PDF that is pretty good at explaining the dtc system. I had a 6 hp scroll that would make a "swoosh" sound when it shut off and then would come right back on like you said. This units cut in and cut out were so close it would short cycle. I widened the differential a bit and cured that problem.

    http://www.pattonnz.com/site/patton/...all_July08.pdf
    Only Chuck Norris can slam a revolving door

  5. #5
    Join Date
    Jun 2006
    Location
    Omaha, Nebraska
    Posts
    843
    If the DTC is not feeding, there may be a high-temp limit stat on the discharge line which will shut the compressor down. If the bulb or cap tube gets damaged and loses the charge then the DTC will not open.

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