What refrigerant condition provides a clear liquid line sight glass?

A clear liquid line sight glass indicates that the refrigerant is in a subcooled liquid state. This condition signifies that the refrigerant has been cooled below its saturation temperature while remaining in liquid form, thus ensuring that no vapor is present in the sight glass.

In practical terms, when the refrigerant is subcooled, it remains entirely in the liquid state, leading to a consistent, clear flow through the sight glass. This clarity is crucial as it confirms that the refrigeration system is functioning correctly, providing an optimal amount of refrigerant for the cooling process.

Conversely, the other conditions mentioned can lead to different appearances in the sight glass. Superheated vapor would appear as a gas, causing the sight glass to look cloudy or show vapor instead of a clear liquid. Saturated vapor may show a mix of liquid and vapor, further obscuring visibility in the sight glass. Partial liquid would indicate that there is a combination of both liquid and vapor present, which would not provide a clear view either. Hence, subcooled liquid is the only condition that guarantees clarity in the sight glass, signifying that the system is operating effectively.