What determines the low side pressure in a refrigeration system?

The low side pressure in a refrigeration system is primarily determined by the amount of liquid refrigerant present in the evaporator. When the evaporator is properly charged with liquid refrigerant, it allows the refrigerant to evaporate effectively, leading to the appropriate pressure in the low side of the system. If there is an adequate amount of liquid refrigerant, it will absorb heat, turn into vapor, and maintain the desired low side pressure effectively.

Alternatively, if the quantity of liquid refrigerant is insufficient, it could lead to issues such as an increase in suction line temperatures and pressure drops. This imbalance disrupts the system's efficiency and cooling capability. Therefore, the relationship between liquid refrigerant volume and low side pressure is crucial for proper system operation.

Regarding the other choices: The size of the evaporator primarily impacts the system’s capacity and efficiency rather than directly determining low side pressure. The total refrigerant charge can influence the overall performance of the system but is not the primary factor governing low side pressure. Ambient temperature can affect the system's performance but does not directly set the low side pressure itself. Hence, the amount of liquid in the system is the most critical factor in establishing and maintaining low side pressure in a refrigeration system.