What component enables a single compressor to control multiple cases at varying temperatures?

The correct choice is the Evaporator Pressure Regulator (EPR) because it plays a crucial role in managing the evaporator pressure, ensuring that different cases can be operated at varying temperatures. The EPR regulates the pressure within the evaporator by controlling the flow of refrigerant based on the temperature demands of the connected cases. This allows a single compressor to efficiently serve multiple cases, maintaining optimal cooling for each individual case according to its specific requirements.

In contrast, other components like the heat exchanger primarily facilitate the transfer of heat between different mediums and do not actively manage pressure or temperature variances across different cases. The compressor pressure regulator focuses on balancing the pressure of the entire system rather than catering to the individual needs of multiple cases. The expansion valve, while important for controlling the flow of refrigerant into the evaporator, does not have the same level of control over maintaining differing evaporator pressures for multiple cases as the EPR does. Thus, the EPR is essential for optimizing performance when multiple units require distinct cooling conditions.