The definition of a mini split icing up is when the indoor evaporator coil of a mini split air conditioning system accumulates too much ice, resulting in a decrease in airflow and a decrease in cooling capacity. This is usually caused by low refrigerant levels, poor airflow, or a malfunctioning thermostat. The ice buildup can cause the evaporator coil to become blocked, preventing air from passing through it and reducing the cooling capacity of the system. In some cases, the ice buildup can even cause the evaporator coil to freeze over, leading to a complete loss of cooling capacity. To prevent mini split icing up, it is important to keep the refrigerant levels topped up, ensure adequate airflow, and regularly check the thermostat for any signs of malfunction. Additionally, it is important to clean the evaporator coil regularly to prevent any dirt or debris from blocking the airflow. If the mini split icing up persists, it is best to call a professional to inspect the system and diagnose the issue.