what is the use sight glass in refrigerators

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Refer here: http://books.google.com/books?id=NAdQGV-imRAC&pg=PA496&lpg=PA496&dq=refrigeration+sight+glass&source=web&ots=voPLvh323i&sig=T6ioamk_u-fZThMHDwlLOH98UBo&hl=en&sa=X&oi=book_result&resnum=3&ct=result

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I used Google Search Engine, just to show you how easy it is: Results 1 - 10 of about 105,000 for refrigeration sight glass. (0.26 seconds)

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Hello guest;

The link Sparkstation sent you to gives a good basic explanation. Sight glasses are useful and in the old days it was just about all we used. To answer what I think you're asking in the second part of your question, and I'm making an assumption here that you have a expansion valve , virtually all walk in boxes do, charge it slowly. The valve will be hunting when you get close to the correct charge.you will see the sight glass flashing and clearing. At that point go grab a cup of coffee a Coke or a beer, and let the valve settle down. Charging by sight glass without allowing the expansion valve to settle down can easily lead to an overcharge or under charged unit.

I would also recommend that you Google superheat and sub cooling, before trying to charger the unit, you might want to consider it is generally a heck of a lot cheaper to hire a servicemen, then to hire a servicemen and by a compressor.

All direct expansion mechanical refrigeration units have either an expansion valve or a capillary tube to regulate the flow of liquid refrigerant into the evaporator. Many years ago, some expansion valves were adjusted by hand in response to changing load conditions. Each evaporator on modern commercial dx refrigeration units is typically equipped with a thermostatic expansion valve, which meters the flow into the evaporator by sensing the presence or absence of liquid refrigerant at the outlet.

Capillary tubes are a cheap fixed metering device, usually used only on domestic refrigerators, freezers, and air conditioners that don't have to respond quickly to big changes in cooling load.

The best use of a sight glass by someone who isn't a refrigeration mechanic is to see whether a unit's failure to cool properly is due to a lack of refrigerant. Trying to service a machine whose operation you don't understand is very risky. It is easy to destroy the valves in your compressor with an overcharge of liquid refrigerant. If the expansion valve is adjusted incorrectly, you don't even have to add refrigerant to the system to do this. Call a service man, please.

You may but that it not the function of the sight glass and it would be dangerous to use in that manner. The sight glass is an indicator of a condition only.

Contact a HVAC service technician and save the lives of everyone in the immediate vicinity up to one mile.

Liquid line sight glasses in refrigerating systems can mislead non technician people. They are installed to show the quantity of refrigerant in the system and are not accurate at all. They will show bubbles in the liquid gas if the system is short of gas, They can mislead by showing bubbles at various times within the cycle when the system still has plenty of gas and the sight glass can show the system full of gas when it may have other problems which emulate a shortage of gas. Mostly the gas should, technically, never have to be replaced or even added to, during the life time of the system. Hope this helps

Phil

sight glasses are used to indicate: the condition of the refrigerant in the plant liquid line, the moisture content in the refrigerant and the flow in the oil return line from the oil separator.

Input from the UK. On a refrigerator or air con circuit there are two coils or "radiators". One is the condensor and the other an evaporator. As the names sugest the evaporator is where the refigerant is evaporated from a liquid to a gas and this is subjected to the heat load being cooled. The condensor then returns the refrigerant back to a liquid using the pressure of the compressor output and suplementary cooling of the ambient air or water cooling towers etc. The condensor will be hot.The sight glass will be positioned just before the thermostatic expansion valve or capillary tube metering the high pressure liquid refrigerant into the low pressure evaporator. In the evaporator the liquid refrigerant is boiled to a gas by the heat load. The sight glass gives a visual indication that liqiud refrigerant is entering the evaporator. As suggested by other replies the superheat of the evaporator and sub cooling of the condensor should also be checked with thermometers.

It is an aid to trouble shoot the system with. Bubbles seen thru the glass may mean that there is a problem. Acquire a qualified service company.

The sight glass indicates the following.

Normally during charging refrigerant you must check and see that all bubbles stop. This is called liquid lock position. The presence of bubbles indicates presence of noncondensable gas. This happens when the system is not properly vaccumed.

In case of leak in ther system the bubbles will show up.

The other condition indicates on sight glass whether system is dry or wet. It must always show dry condition. Wet condition indicates presence of moisture in system and has to be dehydrated before gas charge.