What visual indicator shows that a vapor-cycle cooling system is operating correctly after charging?

A clear sight glass serves as a visual indicator of the proper operation of a vapor-cycle cooling system after it has been charged. When the sight glass is clear, it indicates that there is an adequate amount of refrigerant in the system, and that the refrigerant is flowing properly without excessive bubbles or foam. This clarity signifies that the system is effectively circulating the refrigerant, which is crucial for optimum cooling performance.

In contrast, if there is cloudiness or bubbles observed in the sight glass, it may suggest that there is too much or too little refrigerant, which can lead to potential issues in cooling efficiency, compressor strain, or even system damage. While frost on the evaporator can indicate that the system is functioning, it is typically a sign of low refrigerant or incorrect airflow, and may not necessarily represent proper operation. Continuous compressor noise can indicate operation, but it does not provide the clarity needed to assess whether the system is functioning at the desired efficiency. Low suction temperature is a useful diagnostic tool, but it requires measurement and does not offer a straightforward visual confirmation like a clear sight glass does.