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  1. #1
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    Display case, gravity coil

    Gravity coils are new to me. Just looking for a technical manual or any info on them. Iím curious about the TD, pull down rate, defrost schedule etc.

  2. #2
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    Aug 2013
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    Gravity coils are usually huge in size compared to forced air coils.

    Purpose is to keep humidity up in the case.
    Generally I have seen 15F to 25F TD on most cases with them. Gotta have a higher TD for gravity coils usually

    Sent from my SM-G975U using Tapatalk

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  4. #3
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    Defrost clocks are needed.
    1 1/2 - 2 hours off cycle during closed periods.
    I prefer LP control for temperature control. Cut in corresponds to 38įF

    Remember these are S L O W responding to temperature changes.

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  6. #4
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    Thread Starter
    Thanks man. Iím trying to determine if I have a restricted cap tube or low charge. Unit was in a vacuum and I added a few oz but the pressure wonít rise above 10psi (134a). Itís a little bakery case designed to maintain 36-45 deg. Even at the high end of a 25 deg TD I should be seeing somewhere around 15 psi. And itís running 8psi. Temp is dropping though. Needs a little more diagnostic work....


    Sent from my iPhone using Tapatalk

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  8. #5
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    Gravity coils run lower pressures then forced air. "S L O W L Y" Develop a frost line at the compressor and back it off a few inches!

  9. #6
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    Cap tube..Forget LP for control.

    ETC digital with the sensing bulb buried in the coil. 25 - 35į differential. (you'll have to play with the diff)

  10. #7
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    On True units with gravity coils,
    They use a constant cut in of 35F and cut out at 15F coil temp at the midpoint setting of the control.

    Just a general idea for ya

    Sent from my SM-G975U using Tapatalk

  11. #8
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    I normally shoot for -27/-32’C on gravity coils for refrigeration deli case.
    Defrost is important as you do not want the small droplets of water to freeze under the coil as this effects performance
    The primary function of the design engineer is to make things difficult for the fabricator and impossible for the serviceman.

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  13. #9
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    This is a outstanding Classroom.



    I'm taking notes.
    Hos 4:6 My people are destroyed for lack of knowledge. Because you have rejected knowledge, I will also reject you, that you may be no priest to me. Because you have forgotten your Godís law, I will also forget your children.


    "You've got to Stand for Something or You'll fall for anything" (A. Tippin)


    Mat_15:24 But he answered, ďI wasnít sent to anyone but the lost sheep of the house of Israel.Ē

  14. #10
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    Quote Originally Posted by UmmScott View Post
    On True units with gravity coils,
    They use a constant cut in of 35F and cut out at 15F coil temp at the midpoint setting of the control.

    Just a general idea for ya

    Sent from my SM-G975U using Tapatalk
    I was taught slightly different.

    A good gravity coil job needs an 1 1/2 -2 hr defrost,as pointed out by pecmsg. WHY? Because the gravity coil job builds ice all day long.Next time you get a chance on a gravity coil,start out by seeing what a clean/clear coil looks like right after a defrost. Then watch the coil as the system runs and cools. Frost builds on the coil and fins.Then when the comp shuts off,watch the frost pattern,watch the frost begin to melt,watch the water just start to drip and hang off of the bottom of the fins,watch the comp re-start and see that water drop re-freeze,over and over and over. Finally as the frost/icicle pattern builds & just starts to block the airflow thru the fins/coil its time for the next defrost cycle. One of the big advantages of a gravity coil is the surface of all of those trays filled w/ mayonnaise laced salads does not dry out and get all ugly looking.

  15. #11
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    Quote Originally Posted by TechmanTerry View Post
    I was taught slightly different.

    A good gravity coil job needs an 1 1/2 -2 hr defrost,as pointed out by pecmsg. WHY? Because the gravity coil job builds ice all day long.Next time you get a chance on a gravity coil,start out by seeing what a clean/clear coil looks like right after a defrost. Then watch the coil as the system runs and cools. Frost builds on the coil and fins.Then when the comp shuts off,watch the frost pattern,watch the frost begin to melt,watch the water just start to drip and hang off of the bottom of the fins,watch the comp re-start and see that water drop re-freeze,over and over and over. Finally as the frost/icicle pattern builds & just starts to block the airflow thru the fins/coil its time for the next defrost cycle. One of the big advantages of a gravity coil is the surface of all of those trays filled w/ mayonnaise laced salads does not dry out and get all ugly looking.
    I get that...

    True uses that as their temp control along with a defrost clock with 1 to 1 and a half hour periods to allow the water to drain

    Sent from my SM-G975U using Tapatalk

  16. #12
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    Thread Starter
    This unit was low after all, the cap tube wasnít restricted. I ended up pulling the charge, cutting off the first 6Ē of the cap tube, replacing the FD, vacuuming it down and charging it with the factory charge. It pulled down from 69 deg to 35 deg surprisingly fast. And it ran 8-9psi suction so that must be normal for this unit.

    I kind of suspected it was low from the beginning. And then when I vacuumed it and I struggled to get it below 450 microns I was leaning even more towards a leak. The bummer with this unit is itís totally built in. This was a boutique bakery so of course they couldnít just set a display case on the ground. They had to build it on a pedestal and box it in with an apron front. It does look really nice but I couldnít even clean the condenser coil let alone properly leak check it. So Iíll be back another day with a helper to get it out of there and tear into it.


    Sent from my iPhone using Tapatalk

  17. #13
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    Use the weigh in charge as a starting point, Get the case at or near temp, develop a frost line to the pump and back it off a few inches.

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