When a liquid line is noticeably hot, it probably contains what type of gas?

The presence of noticeable heat in a liquid line indicates that the gas within it has transitioned into a superheated state. Superheated gas is a form of vapor that has absorbed sufficient heat to raise its temperature above the boiling point corresponding to its pressure, thereby becoming very hot without any accompanying liquid.

In the context of refrigeration systems, liquid lines typically carry refrigerant in a liquid state; however, if the line feels hot to the touch, it suggests that the refrigerant has evaporated and turned into a gas, and as it continues to absorb heat, it becomes superheated. This phenomenon illustrates how refrigerants transition through phases in a refrigeration cycle, specifically moving from liquid to superheated gaseous states after leaving the evaporator or during the compression process.

Understanding this relationship helps in diagnosing potential issues in refrigeration systems, as an excessively hot liquid line may indicate improper refrigerant flow or issues with the evaporator or compressor.