An improper refrigerant charge can cause the evaporator coil to operate at a lower pressure and temperature than designed, leading to ice buildup. When the refrigerant level is too low, the coil may become too cold, causing the surrounding moisture to freeze. Conversely, an overcharged system can also lead to ice buildup due to increased pressure and reduced airflow. It’s crucial to ensure the refrigerant charge is within the manufacturer’s recommended specifications to prevent ice buildup and maintain optimal system performance.