If a refrigerant sight glass shows bubbles, what does that indicate?

• A. A Restriction Must Be Causing Flash Gas
• B. There Is Air in the System
• C. There Is Gas in the Liquid
• D. The System Has Too Much Refrigerant

Answer: (C)

Seeing bubbles in the sight glass means there is gas in the liquid. The sight glass is placed in the liquid line to show the quality of the refrigerant heading to the expansion device. If some of the liquid flashes into vapor as it experiences a pressure drop or heats slightly, vapor bubbles form and become visible in the sight glass. This indicates that the liquid isn’t pure liquid anymore and can lead to reduced cooling performance if not addressed. It’s not simply air in the system, and while flash gas can be tied to conditions like charging level or metering behavior, the direct takeaway from visible bubbles is that gas is present in the liquid.