Auto Air Conditioning & Heater Repair: Use of sight glass on air conditioning gauge set., auto air conditioner, liquid refrigerant

Question
I have purchased a set of air conditioning gauges with a sight glass built in. Will this sight glass show foggy when the gauges are connected to an auto air conditioner with a low charge? Or will it only show foggy while adding refrigerant until it is full and goes clear? Just how is this sight glass used?

Answer
Jim,
The sight glass on the gauges themselves is only used to visually verify that the liquid refrigerant is being charged when you charge on the high side of the system. It is also used in conjunction with a portable recovery machine to tell the technician when to switch the recovery machine from recovering liquid refrigerant to recovering vapor refrigerant.
It will NOT determine as to whether your piece of equipment has a low or high charge. The only way to effectively determine that is by comparing your gauge readings and the ambient temperature to a pressure.temperature relationship chart for the specific refrigerant. And it will NOT determine as to when the system is full. Again the only way to determine this with any accuracy is with a p/t chart and a mathematical formula.
Unless you are a technician that will be constantly working in the refrigeration world, you will not use the sight glass on the gauges themselves.
I hope I was of a little assistance, if so please remember to rate this answer. If I can do anything further now or in the future please do not hesitate to ask. Thanks for the question and good luck in everything.