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Thread: Walk-in cooler evap freezing.

  1. #21
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    Quote Originally Posted by Dave0707 View Post
    So the 40 is high but could be in range?
    Dave0707,, The minimum SH of 20*F equates to a short lineset and a longer lineset equates to a higher SH. So w/the CU on top of the WI w/ a real short 3-4-6' lineset you might expect to see a 14-18*F SH.But it is recommended by Copeland to adjust for 20*F SH.

  2. #22
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    The older stats can come out of calibration over time, I like using the digital rancos whenever I get the opportunity. Box been made bigger or larger amount of product being refrigerated is first thing I ask/do. How long does it take to freeze up, how long has it been doing it is some of the first things I'll ask before messing with gauges...air leaks/infiltration can cause headaches on a system that is borderline sized. I've always gone by what I've read here and compromised coil superheat for a 25-40 compressor SH, check other things and maybe consider a 30 minute defrost at 3am or twice a day.
    Last edited by Red850kid; 11-22-2020 at 09:56 PM. Reason: Mispell

  3. #23
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    Thread Starter
    Sorry for not getting back in here sooner. I swapped out the txv and I’m able to now adjust to 20*sh. Perfect.. however it’s still Freezing up- the door seals look tight. The fans run continuously, even when the cu cycles off, I couldn’t even find a breaker to shut them off. There is no thermostat or defrost clock... I believe it shuts off with the pressure switch... I could have it set wrong... but I am leaning towards installing a thermostat, since the box does drop below freezing (at least I can sneak in a few beers and blame it on the cold)

  4. #24
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    Nothing wrong operating off pressure in the right conditions.

  5. #25
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    Quote Originally Posted by Dave0707 View Post
    The fans run continuously, even when the cu cycles off, I couldn’t even find a breaker to shut them off
    Evaporator fans ? They are NOT supposed to shut off , so they appear to be working correctly sir

    I dont like cycling on pressure switches ... but some guys on here can guide you how to set those pressures correctly

  6. #26
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    Thread Starter
    Right, they do not shut off... I couldn’t even find the breaker for it. I would love some guidance as to how to set the pressures on the system, if anyone can help.

    Thanks and happy holidays!

  7. #27
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    Reference a P/T chart. Find the temperature for the refrigerant you're using. Then set the cut-in pressure for the highest temperature you want then the differential or cut-out pressure for the lowest temperature you want.

  8. #28
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    R-12 was 36/16 but that’s a starting point. Every system is unique.
    Is the condensing unit in a controlled environment? Ambient won’t go below 60*F?

  9. #29
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    I think the air coming out of evap will be like 10 deg warmer than the refrigerant.

    So if you are using R22 and you set the low pressure cut-off at 43psi , looking at PT chart thats a 20 deg evap, the air coming out will be 30 deg , so then set the cut - in like 50 psi which is like 28 deg evap coil, so air will be like 38

    But then you have to babysit the unit for a few cycles and watch the thermometer because those are rough estimates

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  11. #30
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    and don't go off of what the needle is pointing at on the control.

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  13. #31
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    Quote Originally Posted by VTP99 View Post
    and don't go off of what the needle is pointing at on the control.
    on those I bend the needle

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  15. #32
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    That's called calibration.

  16. #33
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    Quote Originally Posted by VTP99 View Post
    That's called calibration.
    Like dropping your gauges too zero them out!

  17. #34
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    Quote Originally Posted by Snapperhead View Post
    I think the air coming out of evap will be like 10 deg warmer than the refrigerant.

    So if you are using R22 and you set the low pressure cut-off at 43psi , looking at PT chart thats a 20 deg evap, the air coming out will be 30 deg , so then set the cut - in like 50 psi which is like 28 deg evap coil, so air will be like 38

    But then you have to babysit the unit for a few cycles and watch the thermometer because those are rough estimates
    I set, or used to, r22 cut out at 40 cut in at 60, it worked well


    Sent from my iPhone using Tapatalk

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  19. #35
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    Still need numbers to make any sense out of it.

    The coil only freezes if the coil is below freezing.... so either your low side is too low or your airflow sucks and there’s not enough heat transfer.

    Most walk ins have a TD of 10* so if the box is 37, the refrigerant is 27* which is below freezing but not by much, depending on the humidity needs in the box, you can tweak it.

    Also, where is the SH measurement you speak of? At the comp or the outlet of the evap? They each have different settings but each has to be verified any time a change is made, 20-40* at comp and anywhere between 3 and 13 at the evap depending on the product.

    Please post some pressures and a PT chart for the refrigerant you are using and we can help you better.\

  20. #36
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    Sounds like a good candidate to add a defrost clock.

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