How does a suction line differ from a discharge line in refrigeration?

The suction line and the discharge line serve distinct functions in a refrigeration system, which is why the correct answer highlights the difference in the type of refrigerant they carry. The suction line is responsible for collecting low-pressure vapor refrigerant from the evaporator and transporting it back to the compressor. This vapor has absorbed heat from the environment, and by the time it reaches the compressor, it is at a low pressure.

In contrast, the discharge line transports high-pressure vapor refrigerant from the compressor to the condenser. The compressor increases the pressure of the refrigerant as it compresses it, enabling it to release heat efficiently in the condenser. This significant difference in pressure between the two lines is crucial for the proper functioning of the refrigeration cycle.

Understanding these roles clarifies why the other choices do not correctly describe the differences between the suction and discharge lines. For instance, both carrying refrigerant at the same pressure or being interchangeable would disregard the fundamental principles of refrigerant movement and pressure changes within the system. These differences are essential for maintaining the efficient operation of light commercial refrigeration systems.