What does the compressor control in terms of refrigeration?

The compressor in a refrigeration system primarily controls the pressure of the refrigerant in the high side. It compresses the refrigerant vapor, which increases its pressure and temperature before sending it to the condenser. This process is crucial because it lays the groundwork for the refrigerant to release heat when it moves to the condenser.

While the low side boiling temperature is influenced by the refrigerant's pressure, it is not directly controlled by the compressor itself; rather, it is a result of the operating conditions within the system. Hence, the option stating that the compressor controls the pressure in the high side is the key element of its function, elevating that pressure and enabling efficient heat exchange within the entire refrigeration cycle.