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  1. #1
    Join Date
    Oct 2003
    Location
    Southern California
    Posts
    303

    Measuring Superheat on a Carlyle 06D system

    I'm working on a transport a/c system using R22 and a Carlyle 06D compressor.

    To measure the superheat, the maintenance manual tells us to place the temp probe next to the TXV's temp bulb.
    That's easier said than done, because that area is very hard to get to (only one hand can fit in there). In addition, the TXV's temp bulb is covered with several layers of insulating tape, which can't be removed without destroying it, due to the strong glue.

    So I need another place to position the temp probe. Some textbooks say on the suction line, 6 inches from the compressor. This would work, but its about 6 to 7 feet away from where the manufacture says to place the probe. I don't know how this would affect the superheat reading (the manual's superheat range is 12 - 18 degrees, with 15 being ideal). Is there a conversion factor I need to use, to compensate for the excess length?

  2. #2
    Join Date
    Apr 2001
    Posts
    669
    In that case, I would use the instructions "on the suction line, 6 inches from the compressor". Ideally, 20 to 30F of superheat is what you want at this location.



    Jabs

  3. #3
    Join Date
    Aug 2006
    Location
    st.petersburg,fl
    Posts
    805

    Lightbulb

    Bingo
    Isn't sanity just a one-trick pony anyway? I mean, all you get is that one trick, rational thinking, but when you're good and crazy, well, the sky's the limit!

  4. #4
    Join Date
    Sep 2004
    Location
    Kansas City, Kansas, United States
    Posts
    13,833

    superheat

    yes, make sure that you are fully loaded and check 6" away from the compressor and 25 degrees is great!

    If you are checking at the tev sensing bulb you should have 12 degrees.

    Of course the vapor refrigerant will pick up additional superheat through friction as the refrigerant passes through all those turns and fittings on its way back to the compressor, it might even pick up a little solar gain depending how well insulated the suction line is.
    Then if the compressor is outside on a hot day, with condenser fans pulling 100 degree air across the suction line you might have picked up some more superheat.

    now your 12 degrees of evaporator superheat is 25 degrees compressor superheat. maybe 30.
    I like 25-30, I hate changing compressors due to liquid flood back and it is scientifically proven that refrigerant vapor contains liquid at 9 degrees superheat.
    good luck
    Frank
    I WILL SELL WORK,GENERATE BUSINESS, GO GET NEW CUSTOMERS!
    YOU SHUT THE HELL UP AND QUIT RUNNING YOUR MOUTH!

  5. #5
    Join Date
    Nov 2006
    Location
    North Carolina
    Posts
    130
    Quote Originally Posted by supertek65 View Post
    yes, make sure that you are fully loaded and check 6" away from the compressor and 25 degrees is great!

    If you are checking at the tev sensing bulb you should have 12 degrees.

    Of course the vapor refrigerant will pick up additional superheat through friction as the refrigerant passes through all those turns and fittings on its way back to the compressor, it might even pick up a little solar gain depending how well insulated the suction line is.
    Then if the compressor is outside on a hot day, with condenser fans pulling 100 degree air across the suction line you might have picked up some more superheat.

    now your 12 degrees of evaporator superheat is 25 degrees compressor superheat. maybe 30.
    I like 25-30, I hate changing compressors due to liquid flood back and it is scientifically proven that refrigerant vapor contains liquid at 9 degrees superheat.
    good luck
    Frank


    Where did you get your info on refrigerant vapor contains liquid at 9 degrees superheat, I have never heard this before.

  6. #6
    Join Date
    Sep 2004
    Location
    Kansas City, Kansas, United States
    Posts
    13,833

    superheat

    John Clark C.M.
    John Clark is from compressor manufacturers of America, or something like that!
    He wrote the compressor section in the RSES SAM manuals.
    I think he and Wes Taylor the chief engineer from Carlyle are the two big compressor gurus in the country.
    I think John is a very reliable source.
    Frank
    I WILL SELL WORK,GENERATE BUSINESS, GO GET NEW CUSTOMERS!
    YOU SHUT THE HELL UP AND QUIT RUNNING YOUR MOUTH!

  7. #7
    Join Date
    Mar 2006
    Location
    Pasadena, California
    Posts
    114

    superheat

    Never heard of that statement " superheat at 9 F contains liquid". The Carrier 30RB chillers with EXVs run on 7.5 to 8 f superheatentering the compressor. These are design conditions. In that case all scroll compressors would have to be replaced under warranty.

  8. #8
    Join Date
    May 2004
    Posts
    475
    Friction ?

  9. #9
    Join Date
    Sep 2006
    Location
    Ohio
    Posts
    496
    Quote Originally Posted by 747ken View Post
    I'm working on a transport a/c system using R22 and a Carlyle 06D compressor.

    To measure the superheat, the maintenance manual tells us to place the temp probe next to the TXV's temp bulb.
    That's easier said than done, because that area is very hard to get to (only one hand can fit in there). In addition, the TXV's temp bulb is covered with several layers of insulating tape, which can't be removed without destroying it, due to the strong glue.

    So I need another place to position the temp probe. Some textbooks say on the suction line, 6 inches from the compressor. This would work, but its about 6 to 7 feet away from where the manufacture says to place the probe. I don't know how this would affect the superheat reading (the manual's superheat range is 12 - 18 degrees, with 15 being ideal). Is there a conversion factor I need to use, to compensate for the excess length?
    What I do is make a small cut in the insulation by the TXV bulb to get the line temperature, then cover the cut with foam tape. As far as the difference in line temperatures at the bulb or at the compressor, I have checked at both areas on the same unit with about 7 to 8 feet of well insulated pipe between the two points and only had about 1 degree difference in temperature. But this is on a chiller where the compressor is in the same room as the evaporator.

  10. #10
    Join Date
    Oct 2003
    Location
    Southern California
    Posts
    303
    Quote Originally Posted by hands View Post
    What I do is make a small cut in the insulation by the TXV bulb to get the line temperature, then cover the cut with foam tape.
    That's also a good idea. I'll have to get another temp probe besides my Fluke pipe-clamp type.

    Also, I came across this superheat kit. It might work since my system has a schrader valve right next to the TXV's temp bulb. Anyone use one of these?

    http://www.cdvalve.com/products.asp

  11. #11
    Join Date
    Mar 2007
    Location
    Louisville, KY
    Posts
    22

    Smile Superheat recommendations @ the Service Valve

    You can find everything you need to know about the superheat at the following link.
    http://www.brainerdcompressor.com/superheat.htm

    Hope this helps!

  12. #12
    Join Date
    Jun 2005
    Location
    Ohio
    Posts
    1,720
    Quote Originally Posted by supertek65 View Post
    yes, make sure that you are fully loaded and check 6" away from the compressor and 25 degrees is great!

    If you are checking at the tev sensing bulb you should have 12 degrees.

    Of course the vapor refrigerant will pick up additional superheat through friction as the refrigerant passes through all those turns and fittings on its way back to the compressor, it might even pick up a little solar gain depending how well insulated the suction line is.
    Then if the compressor is outside on a hot day, with condenser fans pulling 100 degree air across the suction line you might have picked up some more superheat.

    now your 12 degrees of evaporator superheat is 25 degrees compressor superheat. maybe 30.
    I like 25-30, I hate changing compressors due to liquid flood back and it is scientifically proven that refrigerant vapor contains liquid at 9 degrees superheat.
    good luck
    Frank
    Frank, are you implying that the refrigerant will absorb 13 degrees (25-12) of superheat while traveling thru a "6-7 foot" suction line? I think this is highly unlikely unless that line is running thru a very high ambient.
    jogas

  13. #13
    Join Date
    Dec 2004
    Location
    Mid-west
    Posts
    567
    The txv companies say there can be liquid droplets in the suction line at superheats up to 6F.

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