The answer to 'why is my ductless system freezing up' is that a ductless system can freeze up due to a few common causes, such as low refrigerant levels, a clogged air filter, or a problem with the system's thermostat or other components. When a ductless system freezes up, you may notice ice buildup on the indoor unit, reduced airflow, and the system shutting off unexpectedly.
Some potential solutions include checking and replacing the air filter, ensuring the outdoor unit is not blocked or obstructed, and having a professional HVAC technician inspect the system for any refrigerant leaks or other issues. Trying to diagnose and fix a frozen ductless system on your own can be tricky, so it's generally best to call in a professional HVAC technician who can properly identify and address the root cause.