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  1. #40
    Join Date
    Jul 2009
    South Carolina
    It sounds more like a dirty evaporator coil or low air flow but I suspect dirty coil. It can still cool O.K. depending on how much demand there is in the conditioned space. A dirty coil won't necessarily show a low TD but will show low SH. I also agree with the others about no need to worry about bubbles in the sight glass, especially dealing with a piston system.
    An engineer designs what he would never work on.
    A technician works on what he would never design.

  2. #41
    Join Date
    May 2011
    Quote Originally Posted by WhiteSoxFan View Post

    FWIW, I had a similar job a month ago. SC was where it was supposed to be but the SG was not clear... I was told a TXV needed a full column of liquid to work properly so I kept adding juice. I couldn't clear the SG to save my life... After way overshhoting the SC and still seeing bubbles, I decided to forget about the SG and just focus on the SC.

    Hope that helps...
    Yep, had a unit early in my career that I charged by site glass, operated great when I left it, next day call for no cool, go back 30* sc, sh&@! Set sc at 10* and no call back. DO NOT CHARGE BY SG, period!!!

  3. #42
    Join Date
    Dec 2010
    Thanks for all of your guys help. Experience says that airconditioning should always have a solid column of liquid, and refrigeration, in low ambient, is the only time you should see bubbles. I think it could be a problem with the piston(in backwards, or moving around a little, like someone mentioned), and probably a few other possibilities, but what are you going to do. If it isn't broke don't fix it. By the way I have checked the evap coil, and it isn't dirty, and I changed the filter. I think the sight glasses should be used in medium and low temp applications only, not air conditioning. Thanks to all.

  4. #43
    Join Date
    Feb 2009
    Tallahassee, FL
    A sight glass is a useful tool on any system regardless of low temp or high temp. IMHO. Its function does not change because it is on a ac unit.

    Its a nice tool meant used in conjunction with (not in leiu of) all the others.

  5. #44
    Join Date
    Jul 2002
    Sightglasses are for TXV systems ONLY. Take it our or tape it up!

  6. #45
    I agree. Sight glasses can be useful on TXV systems but are worthless on fixed bore metering devices. Never use a sight glass on any refrigeration, ac, or heat pump with a fixed bore. Get back to basics and check superheat based upon the inddor dry bulb temp and the outdoor ambient temp.

  7. #46
    Sorry. I meant to say indoor WET bulb and outdoor ambient

  8. #47
    Join Date
    Jun 2004
    Txv or fixed orifice
    Sight glass should not be used to determine the charge on small resi equipment.

    Its not true that only on low ambient condition will cause bubbles on sight glass
    High indoor loads will cause bubbles too
    Dirty condenser
    extreme outdoor temp
    Long liquid line on the roof (flash gas)
    Long vertical liquid line (pressure drop)
    Non condensable
    Blend refrigerant high temperature glide.
    Restriction upstream of sight glass
    Wide txv hunting
    Unseated orifice
    Gas heater is running the same time

    Sorry that's all I could think off right now.

  9. #48
    Quote Originally Posted by shaka View Post
    High indoor loads will cause bubbles too
    Please explain how. Not that I disagree, I just want to understand why.

  10. #49
    Join Date
    Jul 2008
    Mid Michigan
    Quote Originally Posted by WhiteSoxFan View Post
    Please explain how. Not that I disagree, I just want to understand why.
    With more heat to reject at the condensor there will be less liquid building up in the condensor the hot gas will take longer to change state to liquid.
    Waddya mean don't thaw out the frig with a knive?

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