What is the role of a filter dryer in refrigeration?

The role of a filter dryer in refrigeration systems is essential for maintaining the integrity and efficiency of the refrigerant. Specifically, a filter dryer is designed to remove dirt and moisture from the refrigerant. Moisture in the refrigeration system can lead to several problems, including the potential for corrosion, the formation of ice, and the breakdown of refrigerant, which can damage the system components.

By ensuring the refrigerant is free from contaminants and moisture, the filter dryer plays a crucial role in enhancing the overall performance and longevity of the refrigeration system. Contaminants and moisture can significantly affect the system's ability to operate effectively, so the filter dryer is integral to protecting the system from these harmful elements.

In contrast, the other choices refer to functions that do not pertain to the primary purpose of a filter dryer. Adding refrigerant, controlling the compressor, or monitoring system pressure are functions associated with other components of the refrigeration system, such as compressors, gauges, and refrigerant filling devices. Thus, the correct function of the filter dryer is directly related to the removal of dirt and moisture from the refrigerant, ensuring the system runs smoothly and efficiently.