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Thread: Master-Built freezer

  1. #1
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    Master-Built freezer

    Hello all.
    Ive been a HVAC buildings guy for 4 years now. I just transferred to a service building. Now i have 15 walk ins. Coolers and freezers. I am HVAC. But have not worked on allot of Coolers and freezer. More building automation, AHU, Hydronics.

    Here are some specs on the unit.
    It is a Master-Built -10 freezer, with one evap.
    It has been upgraded to a Master controller, with a reversal valve defrost, and a electronic expansion valve.
    Copland compressor, with 404A

    So here's my question. I have a Master-Built freezer with a Copeland compressor in a cabinet on the roof. The cabinet shares condensers with three other compressors. They all share the same condenser coil and fans. So this freezer tripped the pressure switch Last week. I have been told there's been a lot of problems with this unit in the past. When I was looking at it and found that the reversal valve suction lines had a temp difference 25 and 46. So I thought the liquid refrigerant had been leaking into the suction line. At this point I had a close to 10 superheat but the evap temp was -39 and Copeland app called for -25 evap. The outside temp is 56 and the box temp was -8. I replaced the reversal valve and now the superheat is 10 and the evap is -25 perfect. And the box temp is now -10 on the money. But the Copland app is calling for a 105 condenser temp and I'm only getting 80 with no subcool. Im not sure why that is.

  2. #2
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    Never heard of a reversing valve on a freezer. Hot gas solenoid yes.

    Get and read
    https://www.amazon.com/Commercial-Re...rmat=4&depth=1

    SH at the compressor trumps evaporator SH. Maintain 20 - 40F SH at the pump.

  3. #3
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    Thread Starter
    yep.lol
    Its called a Master controller reverse cycle defrost.

  4. #4
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    Thats the t-stat, timeclock, defrost termination, fan delay all in 1 package. Wheres this reversing valve located?

  5. #5
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    The roof top unit

    Cold Zone?

  6. #6
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    Thread Starter
    Well its a bummer i cant send a pic of the diagram on this thing. its page 23 in the manual. But like i Sayed it was (upgraded) It looks like it was a kit. They upgraded the board, exv, and reverse valve.
    Im going to order that book tonight for sure. thanks for that. The reversal valve is on the roof in the cabinet.

  7. #7
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    Thread Starter
    Getting away from the oddity of this unit. Do no why there would be no subcool?

  8. #8
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    It most likely has a receiver so typically we aren't concerned about sub cooling.

  9. #9
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    Quote Originally Posted by pecmsg View Post
    The roof top unit

    Cold Zone?
    I've got one of those by Russell 3 semi-hermetics.
    Came out of a Denny's.

  10. #10
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    Thread Starter
    It does have a receiver. Thank you for that. Question is it better to check superheat at the evap or compressor/condenser?

  11. #11
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    Quote Originally Posted by Brooksmarc View Post
    It does have a receiver. Thank you for that. Question is it better to check superheat at the evap or compressor/condenser?
    Both but compressor sh trumps evap sh
    Honeywell you can buy better but you cant pay more

    I told my wife when i die to sell my fishing stuff for what its worth not what i told her i paid for it

  12. #12
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    Thread Starter
    If you are going to check the SH at the compressor and you had a longer line set isn't kind of a guessing game on SH. I thought the closer you are to the evap the more accurate the number are. Or am I just way off on that?

  13. #13
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    Checking compressor superheat and evaporator superheat are two different things

  14. #14
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    Over 40* at the compressor and the pump over heats, discharge temps clime, oil breaks down. Under 20* and your slugging liquid.

  15. #15
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    With a receiver forget Sub Cooling. Use the sight glass and dont forget about the extra charge for the head master valve thats in there, or at least should be.
    Attached Images Attached Images

  16. #16
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    It's good practice to check superheat at evap. But ALWAYS set superheat at compressor.
    And the reason for setting at compressor is due to variables in the lineset.
    If everything is piped right and insulated perfectly then you'll have perfect superheat everywhere. However I've yet to see a remote condenser that has perfect superheat matching to the evaporator.
    Subcooling really doesn't come into play with a reciever. Superheat only.
    And on this system I'd likely be trying for between 18 and 27 degrees superheat at the compressor
    You don't squat with your spurs on.
    And you NEVER put the torches away before pressure testing.

  17. #17
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    The condenser temp is a function of the outdoor ambient temp, and any low ambient controls. Copeland may have the app with a generic suggestion of 105f liquid saturation temp. But the system has an EEV, which really does not need much of a minumum head pressure.

    So my guess is Masterbilt designed condensing unit to run lower head pressure and take advantage of the energy savings that accompanies lower compression ratios and all that kind of stuff.

    In other words, I would not worry about the low head pressure so long as your sightglass stays clear and system maintains proper operation.

    Sent from my SM-G892A using Tapatalk

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