What is the most likely fault that causes an evaporator on an air conditioning system to freeze solid?

The scenario of an evaporator freezing solid is most commonly linked to reduced airflow through the evaporator itself. When air circulation is obstructed—due to factors such as a dirty air filter, blocked ducts, or fan malfunctions—the evaporator coil cannot effectively transfer heat from the air in the conditioned space. This limited heat exchange can lead to a significant drop in the temperature of the evaporator coil, causing moisture in the air to freeze on the coil's surface. Consequently, as this layer of frost builds up, it restricts airflow even further, ultimately leading to the entire evaporator freezing solid.

Proper airflow is essential for the efficient operation of an air conditioning system, and any reduction in this airflow can initiate a cascade of problems, including the freezing of the evaporator. This emphasizes the importance of regular maintenance, ensuring that filters are clean, and that there are no obstructions in the airflow paths leading to the evaporator.