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  1. #14
    Join Date
    Sep 2008
    Location
    Western PA
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    25,438
    Quote Originally Posted by CommtechinVA View Post
    One guy said subcooling on walk in refrigerator should be 8 degrees.
    A tech asked him and then asked me. I told him it wasn't all that important because you have a receiver. He was bothered by the fact that he got two different answers from the field supervisors. I told him to clear the sightglass and be sure to have some subcooling. As for superheat, I told him 20 degrees at the compressor. I know this can vary but it seems to be a good starting point. This situation is what prompted me to ask you guys what your thoughts are.
    Don't forget that you may need to add flooding charge for low ambient conditions if you have condenser flooding valves.

  2. #15
    Join Date
    Mar 2009
    Location
    Mid-Mo
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    3,594
    Quote Originally Posted by jpsmith1cm View Post
    Once you install a receiver on the system, you're still worried about a solid column of liquid, but the way that you ensure it changes from subcooling measurement to a sightglass.

    So, I guess to answer your questions, subcooling "is what it is" and superheat should to be as low as it can safely run without damaging the compressor.

    X2
    I've been setting ours to 6-10 degrees at the outlet of each evaporator.

    Of course the compressor manufacturers are going to say 20 degrees SSH, they are going to make sure they don't get anything back to the pump. A lot of he larger screws I have worked on run as low as 2-4 SSH.

  3. #16
    Join Date
    Oct 2007
    Location
    Richmond, VA
    Posts
    362
    Quote Originally Posted by jpsmith1cm View Post
    Don't forget that you may need to add flooding charge for low ambient conditions if you have condenser flooding valves.
    I need to research more on flooding valve systems. I haven't ever Dealt with one.

  4. #17
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    170
    I have used these settings for my refrigeration units and have had no problems with these superheat and subcooling values for a starting point, usually they work just fine and dont need much adjusting from there in my experience.

  5. #18
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,266
    Quote Originally Posted by CommtechinVA View Post
    I need to research more on flooding valve systems. I haven't ever Dealt with one.
    Sporlan's Bulletin 90-30-1 is a very good source of info with regards to charging with a flooded head pressure control:

    http://sporlanonline.com/90-30-1.pdf

    The procedure look rather daunting at first, but after you've done it a couple of times it's fairly straightforward.

  6. #19
    Join Date
    Apr 2012
    Location
    Paper Street Soap Company
    Posts
    2,304
    Quote Originally Posted by CommtechinVA View Post
    I need to research more on flooding valve systems. I haven't ever Dealt with one.
    Liebert uses headmasters on their smaller units for low ambient operatjon.

    If not for those units I would have had zero exposure to flooded condensors.

    They are nice enough to put a sight glass on their recievers to make adding its winter charge a snap.

  7. #20
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,438
    Quote Originally Posted by icemeister

    Sporlan's Bulletin 90-30-1 is a very good source of info with regards to charging with a flooded head pressure control:

    http://sporlanonline.com/90-30-1.pdf

    The procedure look rather daunting at first, but after you've done it a couple of times it's fairly straightforward.
    What he said.


  8. #21
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,438
    Quote Originally Posted by Toddbrewster
    I have used these settings for my refrigeration units and have had no problems with these superheat and subcooling values for a starting point, usually they work just fine and dont need much adjusting from there in my experience.
    The point is, there is a right way and a wrong way to do things.

    Your method is not the correct way to charge MOST refrigeration units.

    Read the PDF that icemeister posted. You'll learn something.

  9. #22
    Join Date
    Mar 2012
    Location
    Omaha NE
    Posts
    109
    There is much to learn here. So I am commenting to be able to find this information for later use !

  10. #23
    Join Date
    Jun 2012
    Location
    Wisconsin
    Posts
    118
    The only thing I noticed wrong, maybe I need to be educated, is that for a blend refrigerant you cant charge as gas and you would add charge prior to intial start up on high side. Let system equalize, start unit and then bleed liquid into the low side.

  11. #24
    Join Date
    Jun 2012
    Location
    Wisconsin
    Posts
    118
    If superheat and subcooling dont nescessarily matter in refrigeration, how am I positive I have a solid liquid column to the txv?

  12. #25
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,594
    Quote Originally Posted by Bseliger View Post
    If superheat and subcooling dont nescessarily matter in refrigeration, how am I positive I have a solid liquid column to the txv?
    His point was on a system with a receiver subcooling is essentially not necessary to check. You ensure you have a solid column of liquid by looking at the sight glass and clear the gas. Add the appropriate additional charge for condenser flooding if it had a headmaster valve.

    Superheat values are important but are different than your standard a/c applications, generally speaking.

  13. #26
    Join Date
    Sep 2008
    Location
    Western PA
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    25,438
    Quote Originally Posted by Bseliger View Post
    If superheat and subcooling dont nescessarily matter in refrigeration, how am I positive I have a solid liquid column to the txv?
    With a sightglass...

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