Which factor can lead to a frozen evaporator coil in HVAC systems?

A frozen evaporator coil is primarily caused by low refrigerant levels in HVAC systems. When refrigerant levels drop, there is insufficient liquid refrigerant to absorb heat from the indoor air. This causes the temperature of the evaporator coil to decrease substantially, leading to condensation on the coil that can freeze. As this ice builds up, it further impedes heat absorption and can create a cycle of reduced efficiency, ultimately resulting in the coil being entirely encased in ice.

High refrigerant levels can also lead to problems but would typically result in different issues, such as increased pressure in the system rather than freezing. Good airflow and clean filters are crucial for optimal HVAC performance, as they allow the system to operate efficiently and maintain the necessary temperature differential; however, they do not directly contribute to coil freezing. If airflow is good and filters are clean, these conditions would help prevent a frozen coil rather than promote one.