What does low operating pressures and low system amperage in a residential split system indicate?

Low operating pressures and low system amperage in a residential split system typically indicate low airflow across the evaporator. When the airflow is insufficient, the refrigerant does not absorb enough heat from the indoor air, which can lead to low pressures in the system. As a result, the compressor may not work as hard, leading to lower amperage readings. In HVAC systems, maintaining proper airflow is crucial for efficient operation; low airflow can cause various issues, including inadequate cooling and potential system damage.

The other choices do not accurately account for the symptoms observed. Low refrigerant charge would generally lead to low pressure but may also result in higher amperage as the system struggles to achieve the desired effect. A blocked expansion valve would more likely cause high pressures due to restricted refrigerant flow, while overcharged refrigerant would lead to high operating pressures, contrary to the situation described. Thus, the condition indicated is best explained by low airflow across the evaporator.