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  1. #1
    Join Date
    Mar 2006
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    1,025

    Walk in freezer 404a problem

    New Job. Its on of the stores ill be responsible for, anyway call came in walk in freezer at 20 degs, been at that temp all day, say it was fine before today

    So I get there, verify its running, has a full sight glass, hook up gauges, 50/300, head pressure high, so i clean the coil, no change. Recover some gas (2 pounds) till i started to get bubbles in glass. head pressure still around 300.

    its about 98deg ambient outside. 10deg. subcooling, let unit run for 30mins no change in box temp. Run water over condenser to get the head pressure down.
    Pressure start looking better, 30/225 box cools down to 0deg, before i left.

    Its got a alco style txv, this is what the other tech and I came up with a likely problem, the txv isn't feeding the coil right, and getting alot of liquid coming back up. Or there is a chance it could have some moisture in the system.

    im not a full time refer guy

  2. #2
    Join Date
    May 2000
    Location
    Monmouth Junction-NJ-USA
    Posts
    5,996
    Low side seems kind of high at 50 for a bad valve. Did you take the bulb off and warm it in hand and watch pressure?
    What was the SH at the evap. SH is more importand than SC in refrigeration.
    If you really know how it works, you have an execellent chance of fixin' er up!

    Tomorrow is promised to no one...

  3. #3
    Join Date
    Sep 2006
    Location
    Chicago
    Posts
    474
    Couple things I see... The 300psi head looks about normal for a 98* day. The suction pressure is high for a 20* box. It's hard to say what exactly is going on there. If the txv wasn't feeding or the screen was plugged you would have low suction pressure and lower than normal head pressure. This all doesn't make a lot of sense to me.

    Is this a new store? Is this the first time it's ran in this hot of weather?

  4. #4
    Join Date
    Mar 2006
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    Quote Originally Posted by rayr View Post
    Low side seems kind of high at 50 for a bad valve. Did you take the bulb off and warm it in hand and watch pressure?
    What was the SH at the evap. SH is more importand than SC in refrigeration.
    didnt take it off, but it was mounted right and well insulated, at 50psi thats 15deg, but when it dropped down to 20psi when it was water cooled 20psi is -10below so thats a good pressure for a 0degree box

  5. #5
    Join Date
    Sep 2008
    Location
    Western PA
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    25,397

  6. #6
    Join Date
    Mar 2006
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    1,025
    Quote Originally Posted by jpsmith1cm View Post
    Torch the receiver.
    and what would this do, by heating up the receiver, that would boil more of the liquid to a vapor ? wouldn't that starve the txv more im confused

  7. #7
    Join Date
    Jan 2010
    Posts
    6,075
    The recever has a dip tube that goes to the bottom to pick up liquid only. By torching the recever you will see how much liquid is in there. Should be no more then 80% when it's pumped down.

  8. #8
    Join Date
    Mar 2006
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    Quote Originally Posted by VTP99 View Post
    The recever has a dip tube that goes to the bottom to pick up liquid only. By torching the recever you will see how much liquid is in there. Should be no more then 80% when it's pumped down.
    if its got a dip tube even if the receiver is all the way full of liquid its still going to pick up whats at the bottom though right, the liquid which is more dense would always be at the bottom

  9. #9
    Join Date
    Sep 2006
    Location
    Chicago
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    474
    I don't understand why torch the reciever? With a 98* ambient 300psi would give you a condensing temp of about 118* with 404a. He said he had a full sight glass.

  10. #10
    Join Date
    Jan 2010
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    6,075
    Quote Originally Posted by marter View Post
    if its got a dip tube even if the receiver is all the way full of liquid its still going to pick up whats at the bottom though right, the liquid which is more dense would always be at the bottom
    Yes the liquid is at the bottom. Now if the recever is full it would backup into the condenser which would increase your head pressure. If the dip tube is broken off above the liquid it will feed vapor.

  11. #11
    Join Date
    Mar 2006
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    Quote Originally Posted by VTP99 View Post
    Yes the liquid is at the bottom. Now if the recever is full it would backup into the condenser which would increase your head pressure. If the dip tube is broken off above the liquid it will feed vapor.
    that makes sense, i see the light ... ahhhh so purty
    but by recovering some gas until i dont have a full sight glass, then im ensuring that the reviever is also not overfilled with liquid though, right

  12. #12
    Join Date
    Sep 2006
    Location
    Chicago
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    474
    Quote Originally Posted by marter View Post
    that makes sense, i see the light ... ahhhh so purty
    but by recovering some gas until i dont have a full sight glass, then im ensuring that the reviever is also not overfilled with liquid though, right
    What condensing pressure/temperature would you expect to see with a 98* ambient and a warm box?

  13. #13
    Join Date
    Mar 2006
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    Quote Originally Posted by dangpgt97 View Post
    What condensing pressure/temperature would you expect to see with a 98* ambient and a warm box?
    110*/270psi

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