The refrigerant sight glass can be used to diagnose a restricted filter drier.
What should you look for?
Is the glass upstream or downstream of the drier?
(See the following link for my recommendation.)
If it is downstream, the refrigerant may flash in the glass.
In fact, if the drier is severely restricted, it may never clear!
An unknowing technician may continue to add refrigerant, resulting in an overcharged system.
I have encountered refrigeration systems with extreme amounts of refrigerant, only to find a restricted upstream drier.
What about an upstream glass installation?
A glass installed upstream of a clogged drier, will simply give the opposite indications.
Instead of possible severe refrigerant overcharge, you can encounter a severe undercharge.
The restriction causes the refrigerant to "back up" and clear the glass long before the proper charge is reached.
So, you see, the glass can become useless.
It can be misleading.
What do I do?
I always place my hand on each end of the drier.
Do I feel any temperature difference that could indicate a restricted drier?
If not, I usually trust the glass.
But, within limits!
Years of experience and knowledge of refrigeration equipment, gives one a sense of how much refrigerant a system should hold.
Very small amounts or very large amounts, watch out!
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