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  1. #14
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    14,914
    Quote Originally Posted by beenthere View Post
    If the unit has a charging chart I use it.
    Unless it is a Rheem/Ruud system, and the indoor temp isn't near the normal "comfort" level, or near 50% RH.
    If more government is the answer, then it's a really stupid question.

  2. #15
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,898
    You use the return WB for determining SH.
    Don't take return and supply and mix them together.
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  3. #16
    Join Date
    Apr 2007
    Posts
    623
    Quote Originally Posted by beenthere View Post
    You use the return WB for determining SH.
    Don't take return and supply and mix them together.

    I have been using return wb only, I know others that do the "mix", which I didnt think was right, thanks for the reply.

  4. #17
    Join Date
    Oct 2006
    Location
    Emerald Coast, FL 30.1N 85.8W
    Posts
    681

    superheat relevant for fixed bore or cap tubes

    Most of the TXV systems use subcooling.

    With fixed bore metering, your superheat will usually be between 10 & 20 -- decreasing with higher ambient.

    Amatures use charts -- if your a skilled tech, you shouldn't need a chart.

    I'm an engineer & tech and do 5 to 10 calls a day and never needed a chart -- you either understand air conditioning, or you don't.

  5. #18
    Join Date
    Apr 2007
    Posts
    623
    Quote Originally Posted by emcoasthvacr View Post
    Most of the TXV systems use subcooling.

    With fixed bore metering, your superheat will usually be between 10 & 20 -- decreasing with higher ambient.

    Amatures use charts -- if your a skilled tech, you shouldn't need a chart.

    I'm an engineer & tech and do 5 to 10 calls a day and never needed a chart -- you either understand air conditioning, or you don't.

    The charts only provide the pressure and temp at a glance, they do not explain anything about the operation, I didnt see you mention anything about wet bulb temp,

  6. #19
    Join Date
    Mar 2005
    Location
    reading PA
    Posts
    20

    target superheat

    i realize that if there is a chart in/on the odu its best to use it; but i see alot of units with only subcooling charts on them. if its got a txv, no good. our company will work on anything so i dont have charts from every manufacturer. i ve found a good deal of difference between manufacturers, unit size, and especially freon type. i guess what im really looking for is how everyone feels about the formula i posted originally{ wb x 3 - oat divided by 2 = target superheat }. is it universal?, does it work for all refrigerants? all replies welcome.

  7. #20
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,898
    It will work on any fixed metering device A/C.
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  8. #21
    Join Date
    Feb 2007
    Location
    Dallas, Tx.
    Posts
    572
    Quote Originally Posted by emcoasthvacr View Post
    Most of the TXV systems use subcooling.

    With fixed bore metering, your superheat will usually be between 10 & 20 -- decreasing with higher ambient.

    Amatures use charts -- if your a skilled tech, you shouldn't need a chart.

    I'm an engineer & tech and do 5 to 10 calls a day and never needed a chart -- you either understand air conditioning, or you don't.
    say what!! If you understand A/C- you should know that readings and formulas are critical. I have been blessed over the years to work with some of the best in this business. They understand air conditioning- and they all use charts and meters. Anyone who thinks that they know enough to get by with the hail mary method is not helping anyone out. Return air wet bulb will not only help you calculate target superheat, but proper airflow as well- IF YOU USE THE CHART!
    Last edited by mikelcs; 07-19-2008 at 09:53 AM.
    mike

  9. #22
    Join Date
    Apr 2007
    Posts
    623
    Quote Originally Posted by mknox View Post
    i realize that if there is a chart in/on the odu its best to use it; but i see alot of units with only subcooling charts on them. if its got a txv, no good. our company will work on anything so i dont have charts from every manufacturer. i ve found a good deal of difference between manufacturers, unit size, and especially freon type. i guess what im really looking for is how everyone feels about the formula i posted originally{ wb x 3 - oat divided by 2 = target superheat }. is it universal?, does it work for all refrigerants? all replies welcome.
    The differences you are seeing are between manufacturers, and SEER ratings in the case of Subcooling. R22 and R410A , you are not going to have different requirements just because of the refrigerant used, you may because of equipment efficiency. But that formula works for both refrigerants, difference is, you will probably not see too many 410A systems without a TXV, so you will most likely be using subcooling.

  10. #23
    Join Date
    Feb 2007
    Location
    Dallas, Tx.
    Posts
    572
    Quote Originally Posted by mknox View Post
    so ive seen a number of target superheat charts around but am wondering a calculation ive recently stumbled upon. wet bulb times 3,minus 80, minus outdoor ambient temp.. just wondering if most use a standard chart, try and go by what is on/in the odu, or mabey this calculation? any input is welcome...
    eg. 100* O.A.T., 68*wb R.A.T
    68x3= 204 - 80= 124 - 100* OAT= 24* superheat.
    same conditions w/ the chart I use says target is 12*
    What does everyone else's chart say?
    mike

  11. #24
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,898
    Quote Originally Posted by mikelcs View Post
    eg. 100* O.A.T., 68*wb R.A.T
    68x3= 204 - 80= 124 - 100* OAT= 24* superheat.
    same conditions w/ the chart I use says target is 12*
    What does everyone else's chart say?
    You did it wrong.

    68*3=204,-80=124,-100=24,/2=12

    Target SH is 12F.
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  12. #25
    Join Date
    Apr 2007
    Posts
    623
    Quote Originally Posted by mikelcs View Post
    eg. 100* O.A.T., 68*wb R.A.T
    68x3= 204 - 80= 124 - 100* OAT= 24* superheat.
    same conditions w/ the chart I use says target is 12*
    What does everyone else's chart say?
    You forgot to divide by 2, your target sh is 12

  13. #26
    Join Date
    Feb 2007
    Location
    Dallas, Tx.
    Posts
    572
    i didn't see the /2 on the original post- i got that now
    mike

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