Which of the following can cause a reduction in cooling efficiency in an HVAC system?

A reduction in cooling efficiency in an HVAC system can often be attributed to inadequate refrigerant flow. When the flow of refrigerant is insufficient, it prevents the system from effectively absorbing heat from the indoor air and releasing it outside. This lack of efficient heat exchange results in the system working harder to reach the desired temperature, ultimately causing higher energy consumption and potential system strain.

Inadequate refrigerant flow can occur due to various issues such as blockages in the refrigerant lines, leaks in the system, or problems with the metering devices that control refrigerant flow. Since the metering device is crucial for regulating the quantity of refrigerant that enters the evaporator, any malfunction there can lead to inefficient operation.

This contrasts with the other choices listed, which either indicate optimal conditions (properly sized metering devices, clean air filters, and correct refrigerant charge) or do not impact cooling efficiency negatively. Properly sized metering devices, for example, ensure adequate flow and system performance, while clean air filters support airflow and system efficiency, and a correct refrigerant charge ensures that the system operates as designed without ratio imbalances. Thus, inadequate refrigerant flow stands out as a primary cause of reduced cooling efficiency.