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  1. #53
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,551
    Quote Originally Posted by bluecool View Post
    Its not crap, just its a indication that heat transfer is taking place.
    OK, great. Heat transfer is taking place.

    I don't need gauges to tell me that. My hand will typically tell me that there is a temperature difference between the discharge and the liquid line.

    Still doesn't tell me what I NEED to know about the system.

    That the TXV had a solid column of liquid.

    Since it doesn't tell me that, it is NOT a charging metric.

  2. #54
    Join Date
    May 2011
    Location
    Chas.,WV
    Posts
    30
    Quote Originally Posted by jpsmith1cm View Post
    If the sight glass is after the drier, I'd say it is piped wrong.

    I would agree with DeWalt, EXCEPT for systems with receivers. Once a receiver is added to the mix, you need to clear the glass. If it isn't cleared, it isn't charged right OR you have another problem.
    I believe a case could be made for and against the location of the moisture indicator on the liquid line. All the racks that I work on have the SG located downstream of the drier. Basically as you have indicated, the purpose is to ensure a solid column of liquid , at that point , at least. My point is that used as as part of the diagnosis the SG is valuable.....but , to make a final decision only on a full or bubbling SG will often lead you down the wrong path.

  3. #55
    Join Date
    Sep 2006
    Location
    Chicago
    Posts
    474
    Sight glass should be installed downstream of the filter drier. You can figure out if you're short on gas or the drier is plugged it's not that difficult. Best place for the glass would be at the txv. On some racks you will get bubbles in the sight glass. You will get what looks like a half full glass sitting there. You will get rivering. You don't want to use that as a charging indicator. I think on a large vertical receiver there is turbulance going on in the bottom from the liquid being dumped in the top.

    Now if you're working on a tyler equalizer rack then your sight glass is a proper charge indicator. You have to be careful.

  4. #56
    Join Date
    Mar 2007
    Location
    NW AR
    Posts
    2,478
    Quote Originally Posted by bluecool View Post
    I've never heard of this technique but I'm willing to here more about it. When you say ref temp? Do you mean condenser saturation temp. How can cond. liquid or vapor ever be (-) lower than ambient temp.
    Hes talking about temperature/pressure correlation. The machine must be idle. It must also be pumped down so your not getting a mixed pressure reading from the liquid that may still be in the liquid line inside the conditioned area. Take your pressure and temperature and find it on the chart, just like you would on a container containing an unknown refrigerant.

    Ive tried it and found its still hard to tell, especially on an old r-12 or 502 cooler where a number of refrigerants are very close as far as press/temp correlation.

    If the refrigerant is known as it supposedly is in this instance then non-condensibles would cause the pressure of the r-22 to not correlate with the temperature.
    Last edited by ar_hvac_man; 03-09-2012 at 08:43 AM. Reason: more info

  5. #57
    Join Date
    Feb 2008
    Location
    California
    Posts
    2,065
    On smaller equipment and singles compressor walk-in boxes I usually see it's order as

    1) Filter/Drier
    2) Liquid Solenoid Valve
    3) Liquid/moisture indicator

    Usually all the above items are located inside the condensing unit.

    The sight glass should be full. If you see any bubble in the glass, you would want to take action and look for...

    1) Short on charge
    2) Rapid Liquid pressure/temperature fluctuations (fan cycling)
    3) Restricted filter drier
    4) Restricted liquid solenoid valve

    If it's a pump down system, and you charge to a clear sight glass...you need to make sure the system can pump down without tripping the high pressure control.

    Some systems receivers can't hold the pump down. You could re-locate the liquid solenoid from the condensing unit and put it closer the the evap coil. You gain some additional volume to store pump down in the liquid line.

    I'm getting off track...

    Whether the sight glass is installed before or after the filter, it is a charge indicator. But when installed after the filter, it becomes so much more. and can alert you of a few extra systems problems.

  6. #58
    Join Date
    Dec 2011
    Location
    pensacola fl.
    Posts
    88
    Quote Originally Posted by knave View Post
    easy, killer
    Ok, maybe I should not have taken it so badly. It was my bedtime. However, you can't call something crap without explaining. I'm willing to listen.

  7. #59
    Join Date
    Dec 2011
    Location
    pensacola fl.
    Posts
    88
    Quote Originally Posted by jpsmith1cm View Post
    OK, great. Heat transfer is taking place.

    I don't need gauges to tell me that. My hand will typically tell me that there is a temperature difference between the discharge and the liquid line.

    Still doesn't tell me what I NEED to know about the system.

    That the TXV had a solid column of liquid.

    Since it doesn't tell me that, it is NOT a charging metric.
    Lets look back. You told the guy to charge the system and move on. Did you place your hand on the liquid line? All I saying is head press is one of many observation a tech can use. Head has to referenced to something, normally that is OA. What I would be looking for is not that there is a difference, but the degree of difference between both measurments.

  8. #60
    Join Date
    Oct 2011
    Location
    midwest
    Posts
    58
    Phase Loss, good info... Thats what what I found on this condensing unit... From simple question. Why my head pressure was flacuating. I learned a lot more...

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