What is a common cause for low system subcooling?

Low system subcooling is often the result of a system that is undercharged with refrigerant. Subcooling refers to the process of cooling refrigerant below its saturation temperature after it has condensed. When the refrigerant charge is insufficient, there isn't enough refrigerant in the system to effectively absorb heat, leading to a higher temperature in the liquid line and therefore, lower subcooling.

In an undercharged system, the lack of adequate refrigerant keeps the system from reaching its optimal performance level, where the refrigerant is fully condensed and cooled, which is essential for efficient operation and maintaining cool temperatures in the evaporator. This can result in reduced cooling capacity, potential compressor overheating, and other inefficiencies within the system.

The other factors listed, such as overcharged refrigerant, clogged air filters, and excessive heat exchange, could lead to different issues, but they do not directly cause low system subcooling in the way that being undercharged does. Adjustments to the refrigerant charge can address subcooling issues directly, making this a primary concern when diagnosing such problems.