What could bubbles in a sight glass indicate?

Bubbles in a sight glass typically indicate that there is an undercharge of refrigerant. When the refrigerant level is low, the liquid refrigerant cannot fully occupy the liquid line leading to the evaporator. As a result, some of the refrigerant vaporizes prematurely, creating bubbles that can be seen in the sight glass.

Maintaining the correct refrigerant charge is critical for the efficient operation of an AC system. If the system is undercharged, it may not cool effectively and can lead to greater issues, such as compressor damage over time. Monitoring the sight glass for bubbles can therefore be a valuable diagnostic tool for service technicians.