During the defrosting process, what contributes to the buildup of ice on evaporator coils?

High humidity levels significantly contribute to the buildup of ice on evaporator coils during the defrosting process. When humidity is high, there is an increased amount of moisture in the air that comes into contact with the evaporator coils. As the coils cool down, the moisture in the air condenses and freezes on the coils, leading to ice accumulation. This can disrupt the efficiency of the refrigeration system, as the ice can act as an insulator, further blocking airflow and reducing the system's ability to transfer heat effectively.

In contrast, low refrigerant pressure can lead to insufficient cooling but isn't the direct cause of ice buildup. Improper airflow can indeed cause localized cooling issues, but it is not primarily influenced by humidity levels. Similarly, an inadequate refrigerant charge affects the overall cooling capacity but does not directly correlate with the moisture in the air that leads to ice formation. Therefore, while other factors can impact the performance and efficiency of an HVAC system, high humidity levels play a critical and direct role in the creation of ice on evaporator coils during defrost cycles.