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bubbles in sight glass (6 Posts)
bubbles in sight glassHello All
Why do I commonly see bubbles in the sight glass of refrigeration units when they are properly charged. And if its because the larger size of the sight glass lets some of the liquid flash, why then dont I always see it. And if you say thats because sometimes there is more subcooling, than you might be right!
Bubblesare not normal in any ACR application. The system has to be low on freon or the head press is not being controled at its minimum allowable pressure.
Agree on Disagreement?If an air conditioning or refrigeration system is operating close to its intended target temperature, there should be no bubbles in the sight glass. In other words, if the load on the system is relatively low.
However, if the system is operating under high load, such as in the case of a hot pull down on a refrigeration system or an air conditioning system that is turned on when the indoor ambient is high, bubbles will very likely be present in the sight glass. This is due to the metering device (namely the TXV) opening wide to lower the increased evaporator superheat caused by the high load conditions. This increases the flow rate in the liquid line and can result in some flashing.
An old school of though was to charge systems to a full sight glass all the time. In the case of a hot pull down, charging to a full sight glass will result in a system overcharge. This overcharge often goes undetected since TXV systems typically have receivers that store this excess charge.
So, if your system is operating with bubbles in the sight glass and there is a large load on the system, no worries. However, if the system is operating with low load, then you should not see any bubbles in the sight glass.
Hope this helps.Eugene
bubblesThanks for the response Mr Silberstein.
When you say that "this increases the flow rate in the liquid line" do you mean that the "extra" liquid leaving the liquid line through the txv causes a slight pressure drop in the line and causes flashing? Would i theoretically see bubbles in the entire liquid line as well?
Professor,when I grow up!
MY 2 CENTS WORTHif its a a residential or commericial ac unit or heatpump. Does not matter if its r-22 or 410a learn how to charge the system the right way. boom if it has a tx valve charge by subcooling. bam if it uses a cap tube or fixed orfice use superheat. But u got to make sure your coils are clean.