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Thread: a problem unit

  1. #1
    Join Date
    Jul 2012
    Location
    sanger texas
    Posts
    21

    Confused a problem unit

    hello fellow techs i have a a/c system that has stumped me and would like to see what everyone else thinks. call: not cooling good in afternoon.
    I have a 4 year old 4 ton trane 16seer 410-a heat pump that in the afternoon does not satisfy and has a 4 to 5 degree differance in set point, i have called trane and still awaiting a prognosis. this is my second day on this call so here are the details.

    my first arrival 3:00pm (first day)
    my pressures @ 143/463psig
    40sh-6sc
    ambient temp 104'F
    delta t 19'F return temp 86'F supply temp 67'F
    wet bulb 78.3
    system shows symptoms of low charge due to high superheat and low subcool readings. condensor coil clean washed several times to make sure. decide to return in the morning to see what changes.

    8:30am (second day) system maintaining
    my pressures 121/344psig
    35sh-5sc
    ambient temp 93'F
    delta t 19'F return temp 77'F supply temp 58'F
    compressor amp draw 13.5 fan motor amp draw 0.9 fan is on high speed.
    i decide to charge the system to get 10'F sc and drop my superheat and raise my subcooling at this point my main concern is my head pressure. i decide to return in the afternoon again to see my changes

    3:00pm (second day)
    my pressures are fluxuating between
    154/520 and 149/500psig
    my subcooling and superhead are also doing the same (but much better)
    11-14'F sc - 13-16'F sh
    ambient 104'F
    discharge temp from motor 136'F
    compressor amp draw 20.5 fan motor 1.0
    the system is cooling a little better as you can tell from the superheat and subcool readings, but the head pressure is thru the roof and now my compressor is over amping. i thought maybe reversing valve could be leaking but common suction and suction is same only 5'F difference between c suction and @ evaporator. i dont believe it is the txv due to being able to maintain sh and sc plus when removing the bulb valve opens. also ajusted indoor motor and checked duct work (duck work is a issue but i dont believe it is THE issue) any advise would be much appreciated, oh and system is in cooling second stage

  2. #2
    Join Date
    Jun 2009
    Location
    Pompano Bch, S Fla
    Posts
    57
    Those are some crazy head pressures. Have you considered non-combustibles in the system? Also, it may stupid but have you checked to make sure the valves are comepletely open?
    Good luck

  3. #3
    Join Date
    Jun 2009
    Location
    Pompano Bch, S Fla
    Posts
    57
    You mentioned duct issue. Never underestimate the ducts. Is the handler in the attic? Pulling attic air through the return?

  4. #4
    Join Date
    Jan 2012
    Location
    indy
    Posts
    471
    blocked dryer, check temp drop across dryer, txv?? dont sound like it but if I were to open that system dryer, txv, new freon, I bet your good to go clean the coil too! How old is it, sounds like the motor outside could be getting hot and slowing down, possible yes likely no. If you do have a problem , well we see you do duh, it might be overcharged now, maybe the screen before the txv is partially restricted, still doesnt explain the low subcool though, check fan op and cap very good

  5. #5
    Join Date
    Jul 2012
    Location
    sanger texas
    Posts
    21
    i thought that to maybe it being non-combustables but my superheat and subcool are regulated too well in my opinion to be non-combustables. the issue also happened all the sudden too... not stupid at all i checked both txv valves the outdoor tvx has a bypass which there is no temp rise or drop. and the indoor txv will open by removing the bulb but my head pressure is insane

  6. #6
    Join Date
    Jul 2012
    Location
    NE KS
    Posts
    41
    You might check the TXV versus the Trane recall. I had a similar situation where the TXV was not opening completely. The fact you have a bouncing head pressure would lead me to believe your TXV is acting up.

  7. #7
    Join Date
    Jul 2012
    Location
    sanger texas
    Posts
    21
    Quote Originally Posted by hvacmike85 View Post
    blocked dryer, check temp drop across dryer, txv?? dont sound like it but if I were to open that system dryer, txv, new freon, I bet your good to go clean the coil too! How old is it, sounds like the motor outside could be getting hot and slowing down, possible yes likely no
    checked the dryer is not clogged, checked fan motor okay during all of this running like a camp lol 4 years old

  8. #8
    Join Date
    Jul 2012
    Location
    sanger texas
    Posts
    21
    Quote Originally Posted by Pete954 View Post
    You mentioned duct issue. Never underestimate the ducts. Is the handler in the attic? Pulling attic air through the return?
    that is a issue a big issue but according to the customer it was fine a week ago.. try telling him he needs new duct work, the unit has wall chases i have a 6 degree difference from vent to plenum

  9. #9
    Join Date
    Feb 2011
    Location
    Cloverdale,Ca
    Posts
    316
    Did you clean the condenser coil? Also possible Infiltration of hot air into the return air duct? Make sure airhandler fan on high speed..
    Living the dream !!

  10. #10
    Join Date
    Jan 2012
    Location
    indy
    Posts
    471
    Quote Originally Posted by d.crowder View Post
    checked the dryer is not clogged, checked fan motor okay during all of this running like a camp lol 4 years old
    well with it being under warranty, thats good at least, verify airflow of course, I'd change txv, dryer, change whatever could even be possibly wrong, your time is too valueble to go back 4-5 times, do it while its down, not that I've had to do that much, but there's been a few that I didnt know what part fixed it, but I knew it was fixed

  11. #11
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172
    Where were you taking your temp reading to determine the superheat?? At the TXV bulb or at the condenser? How long is the line set, does it go through a crawlspace or attic??

  12. #12
    Join Date
    Jul 2012
    Location
    sanger texas
    Posts
    21
    condensor coil clean as a whistle, no airflow restrictions what so ever, i changed the speeds on my indoor motor several time to see any change.. none that would make a huge difference... i have a idea but just a idea the 16 seer trane compressor has a bridge rectifier that opens and closes a little between first and second stage (one compressor) but im not quite sure how to check that. im still waiting on a call from trane talk to them once and he told me he'd call back...not a good sign

  13. #13
    Join Date
    Jul 2012
    Location
    sanger texas
    Posts
    21
    Quote Originally Posted by Toddbrewster View Post
    Where were you taking your temp reading to determine the superheat?? At the TXV bulb or at the condenser? How long is the line set, does it go through a crawlspace or attic??
    line set only 25 feet not long at all i took readings everywhere lol, common suction, after reversing valve and suction in at airhandler. for my subcooling before and after dryer in unit and outside of unit

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