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  1. #1
    Join Date
    May 2012
    Location
    Nova Scotia, Canada
    Posts
    41

    Superheat dropping when evaporator loaded?

    Fyi, still in trade school. Working on a small refrigeration trainer (about a 12ft cubed cooler). Instructor had to step out so didn't get a chance to grill him and we're now off 'til Monday. I'll go nuts racking my head over this so that's why I'm coming to you guys.

    After running for 15 mins
    Refrigerant: R-134A
    Suction pressure: 16 psig
    Boiling temp from PT: 16F
    Suction-line temperature: 26F
    Superheat: 10F (Target for these is 8-12)

    After loading (opening cooler doors wide open, for 15 mins)
    Suction pressure: 28 psig
    Boiling temp from pt: 32F
    Suction-line temperature: 36F
    Superheat: 4F ?

    Mind you I'm still learning everything so I'm not ruling out the fact that I could be doing something wrong. What are some factors that may cause this and/or why would my superheat be going DOWN when loading the evaporator? The only thing I could think of was a faulty TXV but I would LOVE some ideas or insight!

    Now that I think on it again, my partner and I may not have properly purged the air from the gauge lines before taking those readings, but would it have this effect?

    Thank you so much for any comments/suggestions.

  2. #2
    Join Date
    Aug 2011
    Location
    Bangalore
    Posts
    21
    What is the static & operating superheat setting for TXV??
    Again check the proper mounting & location of sensing bulb.

  3. #3
    Join Date
    May 2012
    Location
    Nova Scotia, Canada
    Posts
    41
    Thank you for the response. I will check these on Monday and see but I did think the location was fine for the bulb.

  4. #4
    Join Date
    Aug 2012
    Posts
    2,663
    If you are opening the doors you might be disrupting the air flow. If that is the case improper air flow will get you a low superheat.
    My name is TooCoolforschool and I am a chronic over charger.

  5. #5
    Join Date
    May 2012
    Location
    Nova Scotia, Canada
    Posts
    41
    Aha! This makes total sense. So the coil isn't getting enough air flow across it to properly evaporate the refrigerant passing through. Will definitely be playing with that then! I knew there had to be something like that going on I just couldn't piece it together. Thank you much!

    Cheers

  6. #6
    Join Date
    Nov 2011
    Location
    St. Louis
    Posts
    3,411
    Next time heat something in a microwave, if available, or throw a trouble light inside and close the door as far as you can to simulate a load.

    The fact that you were puzzled means you are heading in the right direction. And remember, a wide open TXV is a fixed orifice metering device (should you get a wild hair and throw a lit torch in that cooler).

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