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Thread: pressures

  1. #1
    Join Date
    May 2005
    Location
    carrollton ms
    Posts
    3

    Unhappy

    the ambiant temp is 75 f what should my low and high side pressures be?this on a residetial unit on mobile homes split and package units using r22 i have been out of the buisness for a long time and recently stepped back in and have forgotten alot please help if you can

  2. #2
    Join Date
    Feb 2004
    Location
    Knox CO. KY Occupation: Residintial and Commercial instalation, service,and commercial refrigeration. Interests:4wheeling and Hunting
    Posts
    153
    On a 75 degree day the high side shuold be around 210 psi.
    The low side should be around 68-70 psi. You need to get a temperature/pressure chart, and then take the ambiet temp. and add 30 degrees to that then you can get you pressure for the high side. The low side you want it to be 38-40 degree coil so that would be 68-70 psi.
    GiT-R-Done!!!

  3. #3
    Join Date
    Sep 2004
    Posts
    20
    Add 30 degrees from ambient for high side pressure.

    Low side temp should be 38 - 40.

    Does this rule of thumb work for other refrigerants? i am particularly interested in r134a and r12.

    Where can i get an understanding of what the low pressure and high pressure should be? The books i have now are gobbledygook.

  4. #4
    Join Date
    May 2001
    Location
    Bennington, Vermont U.S.A.
    Posts
    13,864
    Originally posted by nlovas
    Add 30 degrees from ambient for high side pressure.

    Low side temp should be 38 - 40.

    Does this rule of thumb work for other refrigerants? i am particularly interested in r134a and r12.

    Where can i get an understanding of what the low pressure and high pressure should be? The books i have now are gobbledygook.
    To get a good understanding of the gauges and the pressure/temperature relationship you have to do some reading. Look up superheat and subcooling. When you get these two terms down then you'll be able to figure out any refrigerant and what the pressures are supposed to be.

    No matter how old your books are the terms "superheat" or "subcooling" have not changed and are still relavent to refrigeration and air conditioning.

  5. #5
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    You shouldn't charge by pressures alone..........read up on this site.
    If everything was always done "by the book"....the book would never change.

  6. #6
    pressures mean zippo,ziltch,nothing. charging is done by subcooling and superheat.

  7. #7
    Join Date
    Feb 2004
    Posts
    2,597
    the 30 deg. temp over o.a is VERY old school rule of thumb. DO NOT rely on this.

    go to the for your interest section of this site and check out superheat/subcooling.

    good luck.

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