Under what refrigerant conditions will a clear liquid line sight glass be observed?

A clear liquid line sight glass indicates that the refrigerant flowing through the line is in a subcooled liquid state. In this state, the refrigerant is fully condensed and has been cooled below its saturation temperature, meaning it is entirely liquid with no vapor content. This is important because it ensures efficient operation of the refrigeration system and helps to prevent issues like compressor damage, which can occur if vapor enters the compressor.

In contrast, superheated vapor would not show as a clear liquid in the sight glass, as it contains no liquid phase. A mixed phase would also not result in a clear sight glass because it contains both liquid and vapor, leading to a cloudy appearance. Lastly, a saturated vapor would show as a cloudy or undefined look in the sight glass, as it represents a state where the refrigerant is at the boiling point and exists partially as liquid and partially as vapor. Therefore, observing a clear liquid means the refrigerant is entirely in the subcooled liquid state, ensuring proper operation of the system.