How does an expansion valve affect the refrigerant in a system?

The function of an expansion valve in a refrigeration system is to reduce the pressure of the refrigerant as it exits the high-pressure side and enters the low-pressure side of the system. This reduction in pressure allows the refrigerant to expand and cool, which is essential for the refrigeration cycle to function effectively.

When the refrigerant passes through the expansion valve, it undergoes a phase change, transitioning from a liquid to a vapor as it absorbs heat from the environment or the space being cooled. This phase change at reduced pressure is crucial because it lowers the temperature of the refrigerant, enabling it to effectively absorb heat in the evaporator and then cycle back into the compressor.

The other options do not accurately describe the function of an expansion valve. For instance, increasing pressure would be contrary to the purpose of the valve, which is to facilitate cooling by allowing the refrigerant to expand and drop in pressure. Maintaining a constant temperature or directing the refrigerant flow back to the condenser do not capture the primary role of the expansion valve either, which is specifically focused on pressure reduction.