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

The scenario involving the freezing of the evaporator in an air conditioning system is primarily linked to reduced airflow. When airflow over the evaporator coil is insufficient, it prevents the heat exchange process from occurring effectively. This lack of heat transfer allows the refrigerant inside the coil to become overly cold, leading to the formation of ice.

Several factors can lead to reduced airflow, such as clogged air filters, blocked ducts, or malfunctioning fans. This condition is particularly problematic because as ice builds up on the evaporator, it further restricts airflow, creating a cycle that exacerbates the freezing issue.

In contrast, a high refrigerant charge could lead to other operational problems but would not directly result in the evaporator freezing solid. High ambient temperatures would generally prevent freezing, as they increase the thermal load on the system. Using an improper refrigerant type could impact the efficiency of the cooling process but is less likely to cause the specific issue of freezing the evaporator coil. Thus, reduced airflow is the primary fault associated with the freezing of the evaporator in an air conditioning system.