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  1. #14
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    Quote Originally Posted by bibeku View Post
    It was way less than 60*F for sure as the suction line was clearly frosting...
    That's odd, could be an important clue.

    I don't think I have ever seen frost on an ultra low. I've even worked on boxes that go down to - 100゚ C to - 150゚ C, and never any frost. The reason is they use heat exchangers between the suction and the liquid before it enters the metering device. Typically they want to keep all that cooing in the refrigerant rather than moving it through the compressor.

    Maybe they are trying something new, keep the density of the refrigerant up to help protect the compressor, I don't know, just a thought.

    But this could be an important clue. For example, does it use a finned evaporator in the box or is it solid tubing attached to the walls of the equipment. If it is the latter, maybe the piping has become separated from the stainless steel and you are not getting the heat transfer that you should.

    This is the point where you call Revco and asked to speak to an engineer. Asked them if frost on the suction at the compressor is normal. Because like I said, in my experience it is not. For example, is it insulated? If not, then I would guess they are not expecting to see ice there, otherwise there would be a puddle every time the Box shut down.
    I do a triple evac with nitro to remove non condensables.

  2. #15
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    The best thing for you right now would be if they have another similar Box. Then you could look at that and compare.
    I do a triple evac with nitro to remove non condensables.

  3. #16
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    I tend to agree your mixed ratio is not right, too much R134a and not enough of the R404a

  4. #17
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    Quote Originally Posted by BBeerme View Post
    For example, is it insulated? If not, then I would guess they are not expecting to see ice there, otherwise there would be a puddle every time the Box shut down.
    It is fully insulated, so probably they were expecting it to frost.

    Yes, I shall take your advice and talk to a Revco engineer as well.

    But just to think of, what do you feel would be the cause for a zero suction pressure/vacuum even after charging the prescribed amount of refrigerant,

    1. Blockage of lines

    Anything else?

    And if it is point no.1, then is there anyway suction line would still be frosting if suction pressure is 0(sufficient refrigerant is not returning to the compressor).

  5. #18
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    Unfortunately I do not have a similar box to compare with...

  6. #19
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    Quote Originally Posted by Answer-Man View Post
    I tend to agree your mixed ratio is not right, too much R134a and not enough of the R404a
    https://drive.google.com/file/d/1Lkr...ew?usp=sharing

    But, it was mentioned on the name plate...

  7. #20
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    Quote Originally Posted by bibeku View Post
    It is fully insulated, so probably they were expecting it to frost.

    Yes, I shall take your advice and talk to a Revco engineer as well.

    But just to think of, what do you feel would be the cause for a zero suction pressure/vacuum even after charging the prescribed amount of refrigerant,

    1. Blockage of lines

    Anything else?

    And if it is point no.1, then is there anyway suction line would still be frosting if suction pressure is 0(sufficient refrigerant is not returning to the compressor).
    Just take a look at a temperature pressure chart for 404A. If you have a 10゚ temp difference which would put you at -50゚F, I think that will put you just a little bit into a vacuum. Don't have a Temperature pressure chart in front of me right now.

    In fact with a static evaporator, meaning the tubing is somehow secured to the walls of the Box, I would not be the least bit surprised to have a 15 or 20゚ temp difference which would put you even colder than -50゚F
    I do a triple evac with nitro to remove non condensables.

  8. #21
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    In fact, using the temperature difference you may find that your suction pressure is not low enough, which would indicate a weak compressor
    I do a triple evac with nitro to remove non condensables.

  9. #22
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    Quote Originally Posted by BBeerme View Post
    Just take a look at a temperature pressure chart for 404A. If you have a 10゚ temp difference which would put you at -50゚F, I think that will put you just a little bit into a vacuum. Don't have a Temperature pressure chart in front of me right now.

    In fact with a static evaporator, meaning the tubing is somehow secured to the walls of the Box, I would not be the least bit surprised to have a 15 or 20゚ temp difference which would put you even colder than -50゚F
    Oh my... This never occurred to me, you are right. I checked the pressure-temperature chart right now and found that it is -46oC at 0psi and slightly towards vacuum.

    So that might be what is happening in my system, there is blockage and the return of small quantity of refrigerant at 0psi is what is causing the return lines to frost.

  10. #23
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    So there is a good question for the engineers, ask them what sort of temperature difference you are looking for. If they tell you Something like 10, 15 or 20゚, but you have something like 6 or 8゚, that would tell me you probly have a weak compressor.
    I do a triple evac with nitro to remove non condensables.

  11. #24
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    Quote Originally Posted by BBeerme View Post
    So there is a good question for the engineers, ask them what sort of temperature difference you are looking for. If they tell you Something like 10, 15 or 20゚, but you have something like 6 or 8゚, that would tell me you probly have a weak compressor.
    I'll do that... Thank you.

    Also, it is a 12yr old system/compressor, so what are odds you think it'll be a weak compressor?

  12. #25
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    Quote Originally Posted by bibeku View Post
    https://drive.google.com/file/d/1Lkr...ew?usp=sharing

    But, it was mentioned on the name plate...
    What I'm getting at is we are talking about extremely small amounts, 213 grams (7.5 ounces) of r134a and the ability to accurately get that amount measured into the system. All I'm saying on these deep freeze units very small changes in charge can make all the difference if you get what you need.

    Good Luck

  13. #26
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    Quote Originally Posted by Answer-Man View Post
    What I'm getting at is we are talking about extremely small amounts, 213 grams (7.5 ounces) of r134a and the ability to accurately get that amount measured into the system. All I'm saying on these deep freeze units very small changes in charge can make all the difference if you get what you need.

    Good Luck
    Ah.. I see...
    Thanks for your help... I'm just trying to recollect everything I did/happened during the charging process. I will let you know..

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