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  1. #1
    Join Date
    Jun 2002
    Location
    British Columbia, Canada
    Posts
    8

    Post

    I have an R12 walkin cooler charged with R414b.The problem is that my head pressures run too high around 200-225 and I can't get the sight glass to clear.They say with 414, some bubbles are normal but I wonder if the condeser coil or fan are bad. What do you think?

  2. #2
    Join Date
    May 2004
    Posts
    11,994
    I have an R12 walkin cooler charged with R414b.The problem is that my head pressures run too high around 200-225 and I can't get the sight glass to clear.They say with 414, some bubbles are normal but I wonder if the condeser coil or fan are bad. What do you think?

    With HotShot you can forget about clearing your sight glass or you will have an overcharged condition. HotShot is 50% R-22, that is why you will run high head pressures. 180* to 225* are not that unusual depending on your condenser location ambient. HotShot needs good condenser air flow in a wide open area. You may want to consider converting to R-416 if you are in a closed air space.

    If your condenser coil is clean and you have correct fan blade/motor combination turning in the proper direction then there will not be a problem with your condenser coil.

    Here is what I would do assuming you are EPA certified and experienced with such things.
    • Make sure the condenser coil is clean and check the blade direction.
      Check your subcooling at the liquid line out of the condenser coil. (around +10* + - a few)
      Check your superheat at the TXV bulb. (around +20* + - a few)
      Adjust your charge for subcooling first then superheat when the box gets close to cycle temp.


    If you have added HotShot to your system to clear the sight glass, my bet it is overcharged. Check the above first, and then make your adjustments. I am sure you will find the box will run efficiently. If not please get back with us.





  3. #3
    Join Date
    Jul 2004
    Location
    NJ
    Posts
    1,793
    Originally posted by lusker
    Adjust your charge for subcooling first then superheat when the box gets close to cycle temp.[/list]
    [/B]
    lusker could you explain this statement little more?
    would subcooling change as superheat does?
    also charging according to sightglass..is what you said about R 414b true for all 400s?
    in an expansion valve system would you get liquid back to compressor if overcharged?
    thanks.

  4. #4
    Join Date
    Jan 2004
    Location
    Earth
    Posts
    4,879
    I would expect superheat to be around 12 degrees on a walk in cooler.
    A Diamond is just a piece of coal, that made good under pressure!

  5. #5
    Join Date
    May 2004
    Posts
    11,994
    FrozenSolid, Yep, sorry about the brain fart, you are correct. I look for 8* to 12* superheat on a medium temp box.




    Adjust your charge for subcooling first then superheat when the box gets close to cycle temp.


    lusker could you explain this statement little more?
    would subcooling change as superheat does?


    First remember we are discussing a system with a TXV, not a cap tube.

    It will, but very little as you run the system if your charge is adequate. You want to check your system subcooling as the temperature drops in the box drops, not during start up or while the TXV is wide open. Wait until it starts to pinch down. Same goes for superheat.

    also charging according to sightglass..is what you said about R 414b true for all 400s?

    I can’t say, because I don’t use them all. I would need a tractor trailer behind me filled with refrigerant. I do know when you replace R-500 with R-414 you use 100% charge to weight but not sure if it fills the sight glass. Never tried it. I don’t like to use the sight glass when installing a blend. I use subcooling and superheat. Which one you check first depends upon what type of metering system you have.

    in an expansion valve system would you get liquid back to compressor if overcharged?
    thanks.


    If overcharged a little during cool down it is possible, but it highly unlikely as the box is hot. I know you have seen hot boxes run without seeing frost on the suction line but as the TXV pinches off and the longer the box runs the suction line may frost back. This is liquid saturation.

    If overcharged a lot, definitely. It may start with in a few minutes if your compressor runs that long. These are the reasons why we charge to subcooling and superheat.

    Please read the following for more of an understanding of subcooling and superheat.

    http://hvac-talk.com/vbb/showthread.php?threadid=54493

  6. #6
    Join Date
    Jul 2004
    Location
    NJ
    Posts
    1,793
    Originally posted by lusker
    FrozenSolid, Yep, sorry about the brain fart, you are correct. I look for 8* to 12* superheat on a medium temp box.
    Adjust your charge for subcooling first then superheat when the box gets close to cycle temp.
    lusker could you explain this statement little more?
    would subcooling change as superheat does?

    thanks lusker.also I was confused about that 20* superheat.glad that`s corrected.

  7. #7
    Join Date
    Jun 2002
    Location
    British Columbia, Canada
    Posts
    8

    Smile

    Thank's
    It seems it was overcharged.

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