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  1. #1
    Join Date
    Jan 2001
    Posts
    768
    took on this account did pm now starting repairs.units have not been looked at in 5 yrs. up to 7 compressors numerous units flat.anyhow.This is trane rtu the style has 3 cond fans spash coil in supply air stream. repaired leak on condensor coil,replaced drier pulled vaccum to 400 microns.weighed in factory charge.this has two tin cans.the one compressor is out so im trying to charge this with just the one circuit running.Heres what I have245# discharge 55-57 suction 32 deg subcooling 25 deg superheat(is swinging a bit)17 deg split.coils were just cleaned filters ok belts ok. I am guessing problem with txv although I took bulb off and put in hand suction pressure did go up a bit to 65#.

  2. #2
    Join Date
    Dec 2002
    Posts
    9,871

    2 things

    1. Its overcharged. Subcooling should be around 13 degrees.

    2. Locate the txv buld on a horizontal run just leaving the evaporator at the 10 or 2 o'clock position. Check the airflow, adjust the txv to the proper superheat.

    [Edited by rob10 on 06-29-2004 at 08:38 PM]

  3. #3
    Join Date
    Jan 2002
    Location
    Fort Worth\Dallas, Texas
    Posts
    1,703
    Even know you have fair suction you could be overcharged and have a restriction.

  4. #4
    Join Date
    Jun 2004
    Location
    Richmond Virginia
    Posts
    1,078
    I would like to know what the return and supply temperatures were as well as outdoor ambient. It definately sounds like you have liquid stacked in the condenser and you most likely have a defective TXV powerhead. I wouldn't go further with it until the other compressor was installed and you have the system totally up. I have seen the units you are describing (SACA's) with a subcooling circuit in which the liquid lines go through a cap on an extension of the condensate drain and give the unit additional subcooling. If you have this and are in a humid climate this can run up your subcooling. High superheat when a unit has just been started and return air temps are extremely high is not unusual and should be expected. Conversely, if you put a compressor in a unit on a hot afternoon and have a return air temp of 85 degrees from a hot return plenum but your superheat is 12 degrees, you may flood the next morning when the return air temp is lower. Maybe not, it will depend upon the range the valve has. While TXV's react to the suction line temp, the pressure differential does matter as with other metering devices. Generally speaking, the larger the valve, the more this is true.

  5. #5
    32 degrees subcooling means your way overcharged.
    should be around 10 degrees. also if you had a bad powerhead you would not have 50 lb suction pressure.
    suction is low because txv is pinched off

  6. #6
    Join Date
    Jan 2001
    Posts
    768
    I dont know I weighed in factory charge

  7. #7
    Join Date
    Jun 2004
    Location
    Virginia
    Posts
    52
    That much subcooling means either overcharged or a liquid line restriction.The restriction should be obvious.There should be a frost line.could be junk in the txv.I would try to adjust the txv if its adjustable.

  8. #8
    Join Date
    Jan 2001
    Posts
    768
    I weighed in charge. Another tech was hooking up thermometer and I had 18 deg subcooling and I wasnt even close to having factory charge so I guess thats why im leaning towards restriction. I replaced drier so thats ok. I have heard this argument before but what will I see if I have crap in inlet screen to txv.liquid will back up so will I have high subcooling and suction will be lower.If im totaly off base.let me know im still learning.I had a larger unit the other day that you could actually feel tempdifference on liquid drier and thats kinda how that was acting high subcooling high superheat low suction pressure. I havent been back on that (they wanted quote)

  9. #9
    Join Date
    Apr 2004
    Posts
    423

    txv

    this rtu is it an Intellipak? with scroll comp?

  10. #10
    Join Date
    Jan 2001
    Posts
    768
    its an older trane It has three condensor fans. coil slants and filter driers are outside unit under coil.It has a splash coil on supply side of evap coil.I dont think they are scrolls

  11. #11
    Join Date
    May 2004
    Posts
    12,153
    It maybe a BYC130G3L0DA. Had one last week doing similar, but many leaks on the old evap coil. Customer didn't want fixed. New one on the way.

    I bet our resident Trane Guru will know. "txtraneman" where are ya?

  12. #12
    Join Date
    Jan 2001
    Posts
    768
    ill get model and serial that looks familiar

  13. #13
    your not restricted, if you had a dead powerhead or stuck valve or trash ie restriction then you would not have 17 degreesplit and probably not 57 lb suction pressure.

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