Where is the pressure in a refrigeration system changed?

In a refrigeration system, pressure is changed primarily in the compressor and the expansion valve. The compressor increases the pressure of the refrigerant gas, allowing it to circulate through the system. After the refrigerant releases heat in the condenser and becomes a liquid, it passes through the expansion valve, which drastically reduces its pressure, allowing it to evaporate and absorb heat in the evaporator. This pressure change is crucial for the refrigeration cycle to function effectively.