Which of the following factors can lead to increased pressure in a refrigeration system?

In refrigeration systems, an increased pressure can be attributed to a clogged expansion valve. The expansion valve plays a critical role in controlling the flow of refrigerant into the evaporator. When the valve is clogged, it restricts the flow of refrigerant, causing it to back up in the system. This backup leads to elevation in pressure upstream of the valve, which can negatively impact the system's efficiency and cooling capacity.

In contrast, low refrigerant levels generally lead to lower pressures, as there is less refrigerant to absorb heat and generate pressure. Leakage of refrigerant will also typically cause reduced pressure within the system, as the overall amount of refrigerant decreases. Proper airflow is essential for efficient operation, but it does not contribute to increased pressure; instead, it aids in maintaining the optimal pressure conditions necessary for effective refrigeration.