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  1. #1
    Join Date
    Sep 2008
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    4

    Confused meat display case help

    im a hvac tech but unfortanatly i never went to school for refrigeration.. I have a brother who has a little store out in the country and his meat display case keeps freezing up.. the system has r12 in it and i was wondering what thw pressures should read when working appropriately? i know its either low on freon or the defrost timer is bad.. and also would u convert to 134 or use hot shot if it is low on freon??

  2. #2
    Join Date
    Jul 2008
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    27
    Quote Originally Posted by a88ruby View Post
    im a hvac tech but unfortanatly i never went to school for refrigeration.. I have a brother who has a little store out in the country and his meat display case keeps freezing up.. the system has r12 in it and i was wondering what thw pressures should read when working appropriately? i know its either low on freon or the defrost timer is bad.. and also would u convert to 134 or use hot shot if it is low on freon??
    you should recover the R-12 first, then use the hot shot.

  3. #3
    Join Date
    Sep 2008
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    4
    do u know aabout the pressures? im not for sure its low! he can unplug over night and let defrost and them it takes about a month or so to freeze back im thinking its the timer

  4. #4
    Join Date
    Oct 2006
    Location
    Boston
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    57
    The case should be running at 38-40 degrees, so with R12 your back pressure should be roughly 40 ish and R12 has a pretty low head pressure.

    You need a PT chart. LOL

    Just timed defrost? Not electric? Did you check the timer?

  5. #5
    Join Date
    Mar 2007
    Location
    NW AR
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    2,478
    Quote Originally Posted by a88ruby View Post
    im a hvac tech but unfortanatly i never went to school for refrigeration.. I have a brother who has a little store out in the country and his meat display case keeps freezing up.. the system has r12 in it and i was wondering what thw pressures should read when working appropriately? i know its either low on freon or the defrost timer is bad.. and also would u convert to 134 or use hot shot if it is low on freon??
    This is why "Bubba's" should stay out of refrigeration.

  6. #6
    Join Date
    Sep 2005
    Location
    florida
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    5,506
    Quote Originally Posted by a88ruby View Post
    do u know aabout the pressures? im not for sure its low! he can unplug over night and let defrost and them it takes about a month or so to freeze back im thinking its the timer
    I would say that if it take's a month to ice up I would be checking the
    defrost timer first.
    I love the smell of phosgene first thing in the morning:

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  7. #7
    Join Date
    Mar 2007
    Location
    NW AR
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    Yea but first it would be a good idea to learn to diagnose a defrost timer.
    Last edited by ar_hvac_man; 09-24-2008 at 06:14 PM. Reason: verbage

  8. #8
    Join Date
    Sep 2008
    Location
    Cedar Rapids, IA
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    486
    Quote Originally Posted by 537refergirl View Post
    The case should be running at 38-40 degrees, so with R12 your back pressure should be roughly 40 ish and R12 has a pretty low head pressure.

    You need a PT chart. LOL

    Just timed defrost? Not electric? Did you check the timer?
    Its a meat case. They are probably running it at 28 degrees. So suction pressure at temp should be 18-20#

    If its taking a month to freeze up its probably the defrost timer, but it could be the liquid line solenoid is leaking by, or something has happened in the store that raised the humidity level/temperature from what it was before. Maybe they raised the setpoints to save energy? Are all of the fans running ok?

    What kind of case is this? bunker, multideck?????? more info needed.

  9. #9
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    many many things are in play here. So we need some more questions answered. Any time I get asked about deli display cases the first thing that comes to me is to ask if they are gravity or fan coils.

    Gravity defrosts are prone to ice up if defrost not properly applied. Gravity coils need to be suction stop temp control and defrost. Defrost generally runs long, I have seen cases often only clear if on defrost for 110-120 minutes per event. Sounds strange but check any manufacturer of gravity applications and you'll see I am correct.

    fan coils are a bit the same as any other typical set up.

    Superheat is important. Superheat in a deli case is about the most important of any case superheat you'll find your self setting in any application. Freshly prepared cooked food very active with bacteria, almost as bad as dough and yeast and so even refrigeration is essentiall to properly maintaining the perishible product. And if horked up superheats are in play, it can definately cause some of the icing issues.

    Use of case is also important. A lot of times it depends on the case manufacturer, but usually, hot steaming food, prepared, going directly into the case with out first being pre cooled in a hold box, can be huge in icing a coil prematurely.

    Deli cases can be fickle and a sharp guy has to know his stuff.

    I had a customer about a year ago. 60 feet of service deli. Pump down LLSV for defrost and temp control. Each time the case satisfied temp, the LLSV would denergize, it took 15 minutes to stop pumping the case out of all that gas. by the time 5 minutes elapsed, LLSV was calling again. Coil never rested. Now it came to defrost, and half the defrost time, the case was still refrigerating with liquid being pumped out. They thought I was nuts, and I promised not to charge for the call if my plan didn;t work but. I slapped in a suction stop EPR.

    I am treated like a rock star when I go in there now.

  10. #10
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    and see how I totally misread the post, I can imagine my reply was a bit useless. WOW. I am stupid.

    Okay. Like the rest asked. Are we service meat, are we multideck. WHAT the frick is it. lol

  11. #11
    Are you sure it has a defrost timer?

    Basically, its a refrigerator, right? Not a freezer. So it may use off cycle defrost.

    In other words, case is to maintain 38-40'f, and if you do that, the off cycle will allow coil to be above freezing during off cycle allowing any ice to melt.

    BUT, if you run it to cold, it will freeze up. If you know it has a defrost timer, is it just to turn off unit twice a day for 1/2 hr? Try turning up the T-stat a degree or two. Put a good thermometer in there and set it.

    I doubt you have defrost heater elements, but you might. Some cases are converted from other stuff.

  12. #12
    Join Date
    Sep 2007
    Location
    NH
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    1,148
    Quote Originally Posted by Leo3006 View Post
    Are you sure it has a defrost timer?

    Basically, its a refrigerator, right? Not a freezer. So it may use off cycle defrost.

    In other words, case is to maintain 38-40'f, and if you do that, the off cycle will allow coil to be above freezing during off cycle allowing any ice to melt.

    BUT, if you run it to cold, it will freeze up. If you know it has a defrost timer, is it just to turn off unit twice a day for 1/2 hr? Try turning up the T-stat a degree or two. Put a good thermometer in there and set it.

    I doubt you have defrost heater elements, but you might. Some cases are converted from other stuff.


    Never seen a meat case that runs 38-40'f

    If you can't tell the difference between a bad defrost clock and low on charge, I would tell him to call a pro.

  13. #13
    Join Date
    Oct 2006
    Location
    Boston
    Posts
    57
    Quote Originally Posted by Dchappa21 View Post
    Never seen a meat case that runs 38-40'f
    Guess it depends on the application and style. Here all the convenience stores I've worked in the ideal temp for deli was 38-40...maybe we just don't like cold meat. j/k

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