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  1. #1
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    Ammonia evaporator problems

    One of the evaporators I maintain will not defrost completely.
    its set up to be defrosted with hot gas.Ammonia is the refrigerant.
    According to the A4A, during the defrost the coil maintains approximately 75-90 psi.the hot gas period of the defrost is about 40 minutes long.
    Here is what I have tried:
    -Closing the liquid feed shut off valve in case maybe the solenoid was leaking by
    -adding more time to the hot gas portion of the defrost.
    -increased the pressure of the hot gas.
    -closing the suction shut off valve in case the ck2 was leaking by.
    Thus far the only way I've been able to clean the coil entirely is by warming up the ambient temperature of blast freezer the evaporator in question is in,or using warm water to melt the ice.

  2. #2
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    Moved to Refrigeration and Ice Making forum.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  3. #3
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    Are there other air units that keep air circulating while you are defrosting?
    That’s the only thing I can think of.

  4. #4
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    Has the latent load changed?

    Sent from my SM-G950U using Tapatalk

  5. #5
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    How long has this been a problem?

  6. #6
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    Have you actually measured the evaporator pressure to be 75-90 psig during a defrost?

  7. #7
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    Typical temps it appears.
    25 years since I did ammonia so not much help. Heres a screen shot from Parker.

    Sent from my SM-G950U using Tapatalk

  8. #8
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    Thread Starter
    That pressure is based off of the back pressure regulator gauge on the condensate return line.just to make sure the gauge was accurate I replaced it with a brand new gauge and got the same reading

  9. #9
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    Thread Starter
    It's been a problem ever since I got to the plant I'm at.(5 months ago).when it actually started I'm not sure.ive tried to ask that same question to my coworkers and they claim to not know.

  10. #10
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    Thread Starter
    No it's a single evaporator blast freezer

  11. #11
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    Quote Originally Posted by polarey907 View Post
    No it's a single evaporator blast freezer
    Is this evaporator at or near the end of the hot gas line? Does the hot gas line have a means of draining condensate?

    I'm asking that because the hot gas can lose much (or all) of its latent heat as it condense in the piping. As noted in the Parker info posted earlier by icy78, some systems will have a liquid trap at the end of the HG line to keep it drained of liquid.

    It would be helpful to get a feel for what the HG temperatures are at the beginning, middle and end of the defrost period. That would at least tell you if you're at or above saturation temperature.

    I'm not an ammonia guy, but I must say 40 minutes is a long defrost for hot gas.

  12. #12
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    After 15-20 mins would there be any hot gas left ?

  13. #13
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    Quote Originally Posted by VTP99 View Post
    After 15-20 mins would there be any hot gas left ?
    No, if it were a single compressor/ single evaporator system. But I'm assuming it to be in a large central plant.

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