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  1. #1
    Join Date
    Aug 2007
    Location
    East central Indiana
    Posts
    75

    unusual noise at metering device

    I'm a semi-retired HVAC service tech with some install experience. I installed the AC system in my own home with the air handler in the attic. I forgot to put in a liquid line filter drier. Dumb mistake! Anyway, the lineset runs over my bedroom. When the AC runs at night when I'm in bed, I can hear a rattling sound. I've gone into the attic during the day and notice a gurgling, pulsing sound coming from where the lines enter the air handler. The system operates fine. I get pressures 205/62 at 80 degrees ambient with a 23 degree superheat and 13 degree subcool and an 18 degree temperature drop across the Ecoil. Real respectable, I'd say, but I can't help but wonder if something is amiss.

    Any ideas?

  2. #2
    Join Date
    Oct 2003
    Location
    Tampa Bay
    Posts
    131
    Sounds like vapor in the liq. line....double check your charge
    Some people just aren't smart enough to be stupid....

  3. #3
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,846
    Quote Originally Posted by mldncx1 View Post
    I'm a semi-retired HVAC service tech with some install experience. .
    This would be service related problem anyway if there is even a problem, if you go here
    below and fill this out and apply we can help you out more.

    http://hvac-talk.com/vbb/showthread.php?threadid=116113
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  4. #4
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,677
    23 degree superheat sounds kinda high. TXV or Orfice?
    You can't fix stupid

  5. #5
    Join Date
    Aug 2007
    Location
    East central Indiana
    Posts
    75
    I've tried to apply for pro membership before but can't get by the first instruction which is "copy this" I'm a computer idiot and don't know how to do much of anything.

  6. #6
    Join Date
    Aug 2007
    Location
    East central Indiana
    Posts
    75
    It's a fixed orifice.

  7. #7
    Join Date
    Jun 2005
    Posts
    274
    Quote Originally Posted by mldncx1 View Post
    I'm a semi-retired HVAC service tech with some install experience. I installed the AC system in my own home with the air handler in the attic. I forgot to put in a liquid line filter drier. Dumb mistake! Anyway, the lineset runs over my bedroom. When the AC runs at night when I'm in bed, I can hear a rattling sound. I've gone into the attic during the day and notice a gurgling, pulsing sound coming from where the lines enter the air handler. The system operates fine. I get pressures 205/62 at 80 degrees ambient with a 23 degree superheat and 13 degree subcool and an 18 degree temperature drop across the Ecoil. Real respectable, I'd say, but I can't help but wonder if something is amiss.

    Any ideas?
    Looking at the suction pressure and the super heat, it looks a bit undercharged. As a semi retired tech I would guess you know what superheat and approx. suction pressure should be. I don't believe it has anything to do with the liquid line filter/drier.

  8. #8
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,888
    I am curious as to the SEER Rating of the system you installed.
    If it is a 13-SEER or above a 208-psig Head 103-F CST vs a 62-psig suction or a low 35-F temp would not be normal.
    With a 13-SEER a 208 Head would normally get around an 80 or above suction pressure, NOT a 62.

    The sparse data would indicate a "possible" restriction in the liquid line causing vapor in the line, or restricted at the metering device.

    Liquid would back up in the condenser leaving less room & causing increased pressures.

    All of this would cause you to overcharge the system further, thus increasing the head pressure.

    Subcooling can be near normal with a restriction.

    Very low airflow through the E-Coil or a dirty coil & blower wheel would cause a low suction pressure problem but then there would be very low, if any Superheat, which tends to eliminate that fault.

    The surging & pulsating is supposed to indicate non condensibles or vapor in the liquid line.
    http://www.udarrell.com/ac-trouble-shooting-chart.html
    udarrell

  9. #9
    Join Date
    Aug 2007
    Location
    East central Indiana
    Posts
    75
    It's a Bryant 10 SEER system. I bought it "right" when my boss lost his deal with a local builder and had some extras in his floor plan with the Bryant distributor.

    I thought the superheat to be a little high, too. But the subcool looked OK so I let it go.

  10. #10
    Join Date
    Aug 2007
    Location
    East central Indiana
    Posts
    75
    I was afraid that having forgotten to install the filter drier that some flakes inside the lines from brazing might have come loose and be obstructing the metering pin.

    Anyone see that as a possibility?

  11. #11
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,292
    Quote Originally Posted by mldncx1 View Post
    I was afraid that having forgotten to install the filter drier that some flakes inside the lines from brazing might have come loose and be obstructing the metering pin.

    Anyone see that as a possibility?
    It's possible. Wouldn't hurt to pump down and have a look, would it?

    Next time, put in a drier, no matter what, and flow nitrogen while brazing. You might want to go ahead while the system is pumped down and put a drier in, anyway. You're only giving your compressor a better chance at life.

  12. #12
    Join Date
    Aug 2007
    Posts
    24
    Sounds a little low on charge,fixed orifice:charge by superheat. If you pulled a good vac on system,(how many mic's ?)that should eliminate noncondensibles. Did you weigh in charge? Possible pressure drop from line lift to attic (how high?),or kink in liquid line,and flashing vapor. AND what shophound said above(check orifice,put in drier,and use nitrogen when brazing.

  13. #13
    Join Date
    Aug 2007
    Location
    East central Indiana
    Posts
    75

    Thanks!

    Thanks for the tips, guys.

    I plan to pump the system down, blow nitrogen backwards thru the lineset and Ecoil, open up and look at the metering pin, and install a filter drier. I'll let you all know if I find anything.

    I knew better than to put a system together without a filter drier. I just forgot. I also knew better than to braze without low flow nitrogen. I knew better, I just didn't do better!

    Thanks again!

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