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  1. #1
    Join Date
    Mar 2004
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    I read a article by Jim Wheeler on subcooling considerations. He states that a unit with a TXV should have atleast 10* of subcooling, but to achieve even greater efficiency charge until the liguid line temp. reaches the outside temp. or until you notice a significant rise in head pressure whichever comes first. I have a Rheem 12 seer 3 ton system with a TXV. I added refrigerant until the liq. line temp dropped to 98*. Outside temp. was 95*. Liq. line pressure was 295. That gave me about 31* of subcool. Is this system over charged or is it more efficient?

    Thanks coachstace

  2. #2
    Join Date
    May 2002
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    give rheem

    a call it will erase all doubt . Try

  3. #3
    Join Date
    Jan 2004
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    Its sounds like you over charged it.

    Did the temp delta across your coil increase?
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  4. #4
    Join Date
    Oct 2004
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    head pressure kinda high i think... maybe a 200 sounds better..

  5. #5
    Join Date
    Dec 2002
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    When you charge it SC method and the liquid line temp. rises and then starts to drop as your charging then to me you have it overcharged, SC you just subtract the reading on you high side gauge from liquid line temp and I try for anywhere from 10-13 degree difference and leave it alone.
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  6. #6
    Join Date
    Mar 2004
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    Thread Starter
    The Delta T did not increase still at 20* split

  7. #7
    Join Date
    Aug 2006
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    You are definitely overcharged with that type of sub-cooling. Next subject - high head pressure trips.

  8. #8
    Join Date
    Dec 2005
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    what's the low side at?

    seems to me the only thing that's happening is the compressor is working harder just to lose that heat in the condensor.

    ...that's another thing , what's the compressor amp draw?

    [Edited by wolfstrike on 08-15-2006 at 07:10 AM]

  9. #9
    Join Date
    Mar 2004
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    Thread Starter
    The amp draw on the compressor is about 13 amps

  10. #10
    Join Date
    Mar 2003
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    usually newer units have the subcooling rating stamped on the name plate.
    31 degrees is overcharged. the highest i have ever seen is 18 but usually 10.
    but if your not sure just install a sightglass then put a false load like if it were 95 degrees outside and when it clears you should be close

  11. #11
    Join Date
    Jun 2001
    Louisville, KY
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    You don't charge to a clear sight glass on residential systems. You will overcharged. need to register as a pro. This topic needs to be discussed in the professional forum.

    Please register as a PRO, and this thread will be moved to the PRO area.

    Thanks, Benny.
    Perhaps you should have read the instructions before calling.

  12. #12
    Join Date
    Mar 2004
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    Thread Starter
    This is the article I read on SUBCOOLING. My question is by charging the system to achieve more subcooling are you over charging the system or is it more efficient like the article says?

    Subcooling considerations
    Subcooling occurs when the
    temperature of the refrigerant in the
    liquid line is lowered below its
    saturation point. When refrigerant is
    subcooled, there is less heat content as
    it enters the metering devise and thus,
    more cooling is possible. Most
    modern equipment is designed to
    provide 10 or more degrees of
    subcooling, by using larger condensers
    or by addition of subcooling coils.
    So after adding refrigerant to clear
    the liquid line sight glass at normal
    temperatures, you must add more
    refrigerant to provide the necessary
    subcooling. If you fail to do this, the
    equipment will not work to capacity
    and further losses due to liquid line
    “flashing” will occur.
    Subcooling charging method
    The amount of subcooling can be
    determined by checking the liquid line
    temperature and then comparing it to
    the saturated condenser temperature as
    read on a high side gauge. As an
    example: A head pressure of 250 psig
    yields a saturated temperature of
    117*F [using a refrigerant pressuretemperature
    chart or from the gauge
    R-22 scale].
    Charging until the liquid line
    temperature leaving the condenser is
    107*F [in our example] assures at
    least 10* subcooling [117-107=10].
    This [10*] is the amount of subcooling
    specified for many systems, and it will
    seldom get you in trouble.
    However, to achieve even greater
    efficiencies on some systems [where
    subcooling circuits are large enough],
    charge until the liquid line temperature
    at the metering device equals the
    outdoor temperature. Since condenser
    coils are less than 100% efficient, the
    refrigerant temperature leaving the
    condenser will never equal the outdoor
    ambient, but a liquid line that is
    sufficiently long and which runs
    through a cooler outdoor ambient may
    be used to provide additional
    subcooling. You can then achieve
    maximum efficiency by adding
    refrigerant to cool this line, until you
    note some significant rise in head
    pressure or until the line temperature
    reaches outdoor ambient, whichever
    comes first.

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