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  1. #1
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    using sight glasses?

    so Ive seen a few on systems here and there but never really install or use them in my diagnosis or charging etc..

    So what are the all the uses for the sight glass and what do they really tell you?

  2. #2
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    In an ac application, IMO there are two reasons for sight glasses. One is to tell you if you have a moisture in your system and the other is to tell you the condition of the refrigerant at that moment. If you try to charge by clearing the glass only, beware.

    Example: 40 ton rtu, copeland semi compressor. Guy charged the till the glass was clear and left. Next day they called again, out on high head. Unit was running unloaded and he added 30 lbs to a system that only holds 40. We pulled the charge, weighed it back in, all was good.

  3. #3
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    Quote Originally Posted by ryan1088 View Post
    In an ac application, IMO there are two reasons for sight glasses. One is to tell you if you have a moisture in your system and the other is to tell you the condition of the refrigerant at that moment. If you try to charge by clearing the glass only, beware.

    Example: 40 ton rtu, copeland semi compressor. Guy charged the till the glass was clear and left. Next day they called again, out on high head. Unit was running unloaded and he added 30 lbs to a system that only holds 40. We pulled the charge, weighed it back in, all was good.
    so you say clear? I see some with colored indicators and other without but almost all i have seen the liquid running through it , you know churning
    through but it was clear, is that normal? or does that liquid motioning through it like water flowing tell there is air or moisture in the system?

    Bill

  4. #4
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    I've always heard u can charge the system by clearing bubbles from sight glass, that seems to always be the excuse for using them, and of course colored indicators to tell whether there moisture in the system or not. Like the other guy said I wouldn't use it to charge or top off, I've overcharged a couple units in the past using this technique. Better off using superheat or sub cool to charge.

  5. #5
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    If it is installed downstream of the filter drier, you can tell if the filter/drier is restricted by watching for bubbles, indicating metering or flashing of the liquid through the filter/drier. This can be confused with being undercharged though, so be careful.
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  6. #6
    Quote Originally Posted by acguytx View Post
    so you say clear? I see some with colored indicators and other without but almost all i have seen the liquid running through it , you know churning
    through but it was clear, is that normal? or does that liquid motioning through it like water flowing tell there is air or moisture in the system?

    Bill
    You will not "see" the moisture itself. The only way a SG will tell you if there is moisture is by the moisture indicator changing color.
    Not all manufacturers are the same though. IMO, Sporlan is the most common which would have a green color on the moisture indicator for a dry system or yellow if there were moisture present.

    When people say "clearing" the SG they are referring to filling it so that you no longer see vapor. If you can see churning, it means there is vapor present in the SG and you do not have a full column of liquid in your liquid line.

  7. #7
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    Quote Originally Posted by WhiteSoxFan View Post
    You will not "see" the moisture itself. The only way a SG will tell you if there is moisture is by the moisture indicator changing color.
    Not all manufacturers are the same though. IMO, Sporlan is the most common which would have a green color on the moisture indicator for a dry system or yellow if there were moisture present.

    When people say "clearing" the SG they are referring to filling it so that you no longer see vapor. If you can see churning, it means there is vapor present in the SG and you do not have a full column of liquid in your liquid line.
    Good Info, however what does this really mean , if the column doesnt appear full but you have a high head and sc already , obviously you cant add more refrigerant with out popping high head.. what else could this mean or how do you solve the issue?

    thanks in advance..

  8. #8
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    In my past experience a sight glass in a system w/o a TXV or EXV will show bubbles even if it's charged correctly. (In other words, I think they may confuse more than help in a capillary tube fed evaporator.)

  9. #9
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    Bill - most systems are designed to have liquid seal at indoor metering device so if you see vapor in glass than its time to start taking some measurements to see why. The glass is a useful tool IMO. Just not the only one to look to.

    Bubbles in the glass while sc is measured is noncondensibles or error in measurement.

    Or upstream restriction and there is not as much sc as you think.

  10. #10
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    Quote Originally Posted by KnewYork View Post
    In my past experience a sight glass in a system w/o a TXV or EXV will show bubbles even if it's charged correctly. (In other words, I think they may confuse more than help in a capillary tube fed evaporator.)
    Actually a txv or exv will be more prone to running the liquid out. It would have to be extremely high indoor and outdoor and/or dirty od coil to have no liquid seal on a properly charged fixed or txv coil.

  11. #11
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    Quote Originally Posted by SBKold View Post
    Actually a txv or exv will be more prone to running the liquid out. It would have to be extremely high indoor and outdoor and/or dirty od coil to have no liquid seal on a properly charged fixed or txv coil.
    these have 10 ton split systems on roof so evaporators are two circuit txv upflow coils with two txvs to each coil and located below the condensers..maybe that is the reasons? systems are cooling normally at this point but i was wanting to gain more knowledge of these sight glasses for future use..thanks

  12. #12
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    Tpically in the field on large units like these would be coil clogged and possibly undercharged due to tech seeing high pressures.

    How far below are evaps?

    You will actually have liquid pressure gain in the lineset. I want to say it 1/2 psi per foot. (that is what pressure loss is)

    At the handlers the pressure slightly higher than on the roof.

    Maybe these units have internal liquid taps at the handler to get readings there. Pay attention to where driers are located when reading pressure.

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