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  1. #1
    Join Date
    Mar 2008
    Location
    West Monroe, LA
    Posts
    69

    Checking numbers

    Got a 4 ton unit that is acting up on me. Below are my numbers:

    Outdoor DB=92
    Suction Pressure=82
    Discharge pressure 235
    Liquid line temp=110
    Suction line temp=68
    Indoor DB=73.5
    ID WB=64
    Compressor amps 10.5 out of a fla of 14
    Cap tube system

    A superheat of 20 is telling me that I am undercharged when my target should be about 7 degrees. Does this sound like I am on the right track?

  2. #2
    Join Date
    Jul 2012
    Location
    San Francisco Bay area
    Posts
    90
    Whats the delta T across the evap

  3. #3
    Join Date
    Mar 2008
    Location
    West Monroe, LA
    Posts
    69
    10 degrees

  4. #4
    Join Date
    Jul 2012
    Location
    San Francisco Bay area
    Posts
    90
    little low on charge just need to recheck the superheat after space temp gets down to setpoint

  5. #5
    Join Date
    Jul 2012
    Location
    San Francisco Bay area
    Posts
    90
    go for 12 sh

  6. #6
    Join Date
    Jan 2012
    Location
    WEST COLUMBIA S.C.
    Posts
    279
    What type of metering device and what is your supply and return temp.I ASSUME this is a R22 system based on pressures?

  7. #7
    Join Date
    Mar 2008
    Location
    West Monroe, LA
    Posts
    69
    Cap tube system with 73.5 return and 64 supply. It is an r-22 system.

  8. #8
    Join Date
    Nov 2010
    Location
    N. Idaho
    Posts
    586
    My TSH shows somewhere around 7, with the conditions you stated. I'd say you're on the right track
    "I've got my Gas Mechanics license"
    "Yea, well my 16yr old daughter has her drivers license, doesn't mean she knows how to drive"

  9. #9
    Join Date
    Dec 2005
    Posts
    3,987
    Is the ductwork tight?

  10. #10
    Join Date
    Jan 2012
    Location
    WEST COLUMBIA S.C.
    Posts
    279
    What is your cfm at return

  11. #11
    Join Date
    Jul 2005
    Posts
    5,574
    You have a bad (under-pumping) compressor. High suction, low head, low amp draw, low deltaT. Adding refrigerant will only run the suction pressure up higher, and it's already way to high for those conditions on an old cap tube system.

  12. #12
    Join Date
    Jan 2012
    Location
    WEST COLUMBIA S.C.
    Posts
    279
    X2

  13. #13
    Join Date
    Jul 2009
    Location
    South Carolina
    Posts
    3,245
    The only way it would be undercharged is if you were sucking air from the attic across the evaporator. If the temps you measured are what are actually going across the evaporator then I agree with Hvacrmedic, you have a weak compressor.
    Gary
    -----------
    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

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