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  1. #27
    Join Date
    Oct 2008
    Location
    florida
    Posts
    138
    super heat is only posible when there is no liguid present other wise you have a saturated gas ie liquid and vapor present which would be the temperature on your p/t chart.so the liquid has to be boiled off before the vapor can be super heated.hope this helps.

  2. #28
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,567
    Quote Originally Posted by btcstudenthvacr View Post
    Most compressors are not capable of pumping liquid is doesn't compress it hydraulics in the pump and destroyes the pump.
    Hermetic compressors are cooled by suction gas.
    BINGO! There should NEVER be liquid refrigerant in the compressor. If there is, you have a major problem. Even less so an air cooled compressor. The refrigerant gas runs directly into the cylinder rather than passing over the windings first. A refrigerant cooled compressor can forgive an occasional dribble of liquid back the suction line, an air cooled will make quick scrap if you allow liquid in.

    If you have even 1 degree of superheat, by definition, you cannot have liquid present in the line. I have gotten into heated debates with people over this, usually people who didn't study hard enough in tech school. Several seasoned techs that work for my company believe that there should not be ice on suction lines, EVEN ON FROZEN FOOD!!! I have talked myself blue in the face trying to explain that to manage that on a -23F rack, keeping the lines ice free requires 55 degrees of superheat to the compressor. Do the math. You can have lines at -3 degrees and still have 20 degrees superheat at the compressor which is the manufacturer's recommended minimum superheat. If you've got a -3 degree line, you WILL have ice buildup on that line.

    That is where your compressor cooling comes from, not liquid, but superheated vapor that is still cooler than the motor windings.

  3. #29
    Join Date
    May 2007
    Location
    Alabama
    Posts
    909
    Quote Originally Posted by adammemin View Post
    Yes that is correct even though the compressor is air cooled the the compressor still needs a small amount of liquid coming back to cool the windings. Someone please correct me if you feel im wrong....
    I was going to, everybody else beat me to it! Suction line+liquid=forked compressor! Even though scrolls can handle some, not a good thing to have!

  4. #30
    Join Date
    Mar 2005
    Posts
    664
    schreader core remover tool with inline thermometer " kit ", as accurate as you will ever get regards stan
    Keep it simple to keep it cool!

  5. #31
    Join Date
    Feb 2008
    Location
    Waffleville
    Posts
    10,339
    Quote Originally Posted by adammemin View Post
    The compressor needs that liquid to keep it cool.
    maybe we should start at, what is the definition of superheat?

    anyone here wanna take a stab at it?

    i am pretty sure the word liquid is nowhere in that def.
    If Guns Kill People, Do Pencils Misspell Words?

    http://www.youtube.com/watch?v=An2a1...eature=related

    Before we work on artificial intelligence why don't we do something about natural stupidity?

  6. #32
    Join Date
    Feb 2008
    Location
    Waffleville
    Posts
    10,339
    Quote Originally Posted by stanbyyourword View Post
    schreader core remover tool with inline thermometer " kit ", as accurate as you will ever get regards stan
    yellow jacket makes the kit i have
    If Guns Kill People, Do Pencils Misspell Words?

    http://www.youtube.com/watch?v=An2a1...eature=related

    Before we work on artificial intelligence why don't we do something about natural stupidity?

  7. #33
    Join Date
    Aug 2007
    Location
    South central WI
    Posts
    257
    Quote Originally Posted by beachtech View Post
    maybe we should start at, what is the definition of superheat?

    anyone here wanna take a stab at it?


    i am pretty sure the word liquid is nowhere in that def.
    Superheat is the sensible heat added to the refrigerant vapor after the change of state has take place. Off the top of my head. Had a test of evaporators today got an A...Half was hands on and half was mental and paper...

  8. #34
    Join Date
    Apr 2008
    Location
    Central CA
    Posts
    567
    Well to have superheat by definition you cant have liquid only superheated vapor.
    If there was no superheat then there is liquid ie in the saturated state and you will have what i like to call a "DCP" dead compressor pumping because its only a matter of time
    Its the superheated vapor that cools the motor windings and removes the heat of compression at the same time.

  9. #35
    Join Date
    Aug 2007
    Location
    South central WI
    Posts
    257
    Quote Originally Posted by stomper56 View Post
    Well to have superheat by definition you cant have liquid only superheated vapor.
    If there was no superheat then there is liquid ie in the saturated state and you will have what i like to call a "DCP" dead compressor pumping because its only a matter of time
    Its the superheated vapor that cools the motor windings and removes the heat of compression at the same time.
    What I already said

  10. #36
    Join Date
    Apr 2008
    Location
    Central CA
    Posts
    567
    Quote Originally Posted by btcstudenthvacr View Post
    What I already said
    So whats your point, this isn't a competition i posted it for others so they might understand it better

  11. #37

    Hmm Superheat

    Here is the key factor that most of us out in the field take superheat, which is to verify the charge on a system. Especially on a older system that may have lost some of it's capacity. Taking your temp reading at the evaporator on the suction line & the other is 6" to 8" from the compressor. I have tried both & have not gotten good readings, even on a new system. Have any of you had better lucky? If you have, then where did you take your temp at?

  12. #38

    The best way to check superheat

    Line clamp temperature probe mounted and insulated at TXV bulb location at 10:00 or 2:00 position on suction line.

    For pressure, access fitting at evaporator outlet, if access fitting at compressor add 2 psi to compensate for line pressure loss.

    Temperature corresponding to refrigerant pressure reading is subtracted from temperature of line probe and the resultant is superheat.

  13. #39
    Join Date
    Aug 2005
    Location
    Bangor Maine
    Posts
    164
    is there a cut out for mobile homes?

    Quote Originally Posted by jdaug1 View Post
    Good link Lusker!

    This one is my fav.

    http://www.hvaccomputer.com/hvac/sizer.asp

    roflmao!

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