The answer to 'why is my ductless system freezing up' is that a frozen evaporator coil is a common issue with ductless HVAC systems. This can be caused by low refrigerant levels, a blocked air filter, or a malfunctioning thermostat or blower fan. Symptoms include ice buildup on the coil, reduced airflow, and poor cooling performance.
If the coil is frozen, the first step is to turn off the system and allow the ice to fully melt. Once melted, check and replace the air filter if needed. You can also try increasing the thermostat temperature setting to see if that allows the system to cycle properly. However, if the issue persists, it's best to call a professional HVAC technician to diagnose and repair the problem, as they have the tools and expertise to properly service a ductless system.