Final answer:
The expansion valve in a compression refrigeration system senses the temperature of the refrigerant vapor leaving the evaporator, which is crucial for regulating the refrigeration cycle.
Step-by-step explanation:
The expansion valve in a common compression refrigeration system primarily senses the temperature of the refrigerant vapor leaving the evaporator. It is part of a refrigeration cycle, which also includes a compressor, condenser, and evaporator. The compressor increases the temperature and pressure of the refrigerant gas, which then transfers heat to the surrounding space as it condenses into a liquid in the condenser coils. After condensation, the refrigerant passes through the expansion valve, where it is cooled upon expansion and then returns to the evaporator to absorb heat from the refrigerated space and complete the cycle.