Sight glasses
You fit a sight glass in the liquid line of an air conditioning system. It shows whether there are bubbles in the refrigerant flow and whether the refrigerant is wet. When charging, flushing or checking a system you need that view. Sight glasses come with different connections. Measure the pipe or the service port where the glass goes and take that measurement with you when ordering. For R1234YF and R134A there are ready-made kits with a glass, a hose and the couplings included. You connect them to the service ports of the system. If you use UV leak detection, a UV lamp also shows you where dye is escaping from the system.
Choosing sight glasses for aircon service
Which connection fits your system
Sight glasses come with different connections. Measure the pipe or service port where the glass goes and take that measurement with you. For R1234YF and R134A there are ready-made kits with a glass, a hose and the couplings included. You connect them to the service ports of the system. That saves you hunting for a matching combination part by part.
When to replace a sight glass
A glass that has gone cloudy or that you can no longer see through tells you nothing about the charge. Replace it then. If there is moisture in the system, it settles on the glass and you see a haze. That is the moment to have the system dried out and to include the glass in the service. Fit a new glass with the correct couplings and hoses so the connection stays sealed.
Sight glass or diagnostic kit
A separate sight glass is fixed into a pipe. A visual diagnostic kit for R1234YF or a visual diagnostic kit for R134A is used during servicing. With it you look at the refrigerant flow without opening the system. Which of the two you need depends on the refrigerant in the system. Check that first on the aircon's type plate.
Visibility during UV leak detection
If you work with UV oil or dye, a clear view of the pipes matters. A sight glass shows the flow, a UV lamp shows where dye is escaping. Together they point you to the spot you need to be. If you use a UV lamp, put on UV glasses to protect your eyes from the ultraviolet light.