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  1. #1
    Join Date
    Jun 2001
    Location
    Northwest Indiana
    Posts
    1,302

    RTAA070 Low Superheat

    M# RTAA0704XR02A3CO GNBF
    S# U06A05763

    This one puzzels me, considering i dont get out much I guess its no surprise:|
    cIRCUIT #1
    Measured suction at Charging port 80psi
    Displayed pressure on unit 115psi
    checked out both suction and compressor sensor per manual. voltage was spot on to actual measure temperature.

    Start machine, 39%load, instantly jump to 50% back down to 45%
    compressor amps approx 26
    suction pressure stayed in the 75-80 range(guage)
    head pressure stayed arounf 200(guage), discharge line At compressor luke warm at best.
    displayed pressures on unit
    suction 110.6
    head 217.6
    cmpressor suction fefrigerant temp 43.9F
    saturated evap fefrigerant temp 63.5f
    water inlet approx 54
    outlet 49
    it takes about 3min to shut down on low superheat
    motor end cold and sweating.

    Again i did verify the sensors and they passed. not sure how this thing calculates superheat.
    i read up on the female and male unloader but i think trane made it extra confusing just for me.
    Any thoughts are greatly appreciated
    oh, outdoor ambient hovering 95-100F

    thankyou
    If you cant fix it right, try again.

  2. #2
    Join Date
    Jan 2009
    Location
    Not in Iran
    Posts
    1,076
    suction sounds a little high,

    is this an r 22 machine

    overcharged maybe?
    no signature blast'em man blast'em
    !!!KILL THE TERRORIST!!!

  3. #3
    Join Date
    Jul 2007
    Location
    The Hot South
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    If you verified sensors and they are good then your saturated evap and compressor suction temp sensors are wired in backwards. Your comp suction temp can't be lower than your saturated evap temp. It's impossible to have 20 deg reverse superheat.

  4. #4
    Join Date
    Jun 2001
    Location
    Northwest Indiana
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    Quote Originally Posted by R123 View Post
    If you verified sensors and they are good then your saturated evap and compressor suction temp sensors are wired in backwards. Your comp suction temp can't be lower than your saturated evap temp. It's impossible to have 20 deg reverse superheat.
    i took a video of all parameters let me double check that
    If you cant fix it right, try again.

  5. #5
    Join Date
    Jun 2001
    Location
    Northwest Indiana
    Posts
    1,302
    Sensors are not flip flopped. i verified that. for some reason the compressor crankcase is filling up with lots of liquid and thats why the lower temp.
    this compressor is very quiet, something is "facotchulated" in there.
    i have learned the hard way over the years that nothing is impossible

    Thanks for your input on this
    If you cant fix it right, try again.

  6. #6
    Join Date
    Jul 2007
    Location
    The Hot South
    Posts
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    From the data your posting, it sure looks like your saturated evap refrigerant temp sensor is reading high. If your getting 80 PSI with gauge, that's 48 deg, which is inline with your leaving water temp (1 deg approach). How many circuits are running? Your refrigerant temp has to be lower than your water temp.

  7. #7
    Join Date
    Jun 2001
    Location
    Northwest Indiana
    Posts
    1,302
    EXV position is controlled by those 2 sensors
    it makes sense that it would be wide open.
    i dont understand why its convering to 110 psi on the display
    is their another transducer im missing?
    i took the voltage readings with the circuit off
    If you cant fix it right, try again.

  8. #8
    Join Date
    Jul 2007
    Location
    The Hot South
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    How did you check the sensor?

  9. #9
    Join Date
    Jun 2001
    Location
    Northwest Indiana
    Posts
    1,302
    measured voltage at ucm, measured actual temp with infared and compared on the chart
    i meant to say compressor was not running when i said circuit was off
    If you cant fix it right, try again.

  10. #10
    Join Date
    Dec 2009
    Location
    Fort Worth, Texas
    Posts
    151
    laser thermometer is your problem. what is your subcooling, becuase if your thermistors are acurate then your overcharged or the exv is stuck open.
    we need subcooling value also your about to install a new compressor they dont like liquid

  11. #11
    Join Date
    Jun 2001
    Location
    Northwest Indiana
    Posts
    1,302
    Quote Originally Posted by HJ Controls View Post
    laser thermometer is your problem. what is your subcooling, becuase if your thermistors are acurate then your overcharged or the exv is stuck open.
    we need subcooling value also your about to install a new compressor they dont like liquid
    my laser is dead nuts, no offense, but i will verify with a good strap on tomorrow as any is posssible;0)
    didnt run long enough for me to care about sub cooling, plus all the liquid flooding back
    unit only runs 3 min till lock out.
    i went in to servicde and locked out that compressor
    ill buy the exv is stuck open.
    i gotta prove tomorrow though.
    If you cant fix it right, try again.

  12. #12
    Join Date
    Jul 2007
    Location
    The Hot South
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    Using an infared to check these sensors will give a false reading. When you compare suction pressure using gauge to display pressure, it shows at the sensor is bad. Im assuming you took these readings with circuit running.

  13. #13
    Join Date
    Jul 2007
    Location
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    It's against the laws of physics to have 20 degrees negative superheat.

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