What condition would cause an evaporator to freeze up?

An evaporator can freeze up due to low refrigerant levels. When the refrigerant level is low, there is inadequate refrigerant available to absorb heat effectively from the indoor air. As the system operates, the diminished level of refrigerant leads to a drop in pressure within the evaporator. This can cause the temperature of the refrigerant to fall significantly, resulting in the evaporator coil reaching temperatures below freezing. Consequently, moisture in the air condenses on the coil, and as this moisture accumulates, it freezes, leading to the coil becoming iced over. This condition not only affects the efficiency of the cooling system but can also impede airflow and potentially result in system damage if not addressed.

In contrast, excess humidity in the air may cause condensation but does not directly lead to freezing unless accompanied by other issues such as low refrigerant. High airflow over the coil is usually beneficial for heat transfer and can help prevent freezing, as it increases the heat exchange. Lastly, having a high temperature for the refrigerant typically ensures that the system operates efficiently and prevents freezing, which further emphasizes why low refrigerant levels are critical to monitor to avoid this issue.