The answer to 'why is my mini split freezing up' is that a frozen coil is a common issue with mini split air conditioners. This can happen when the refrigerant flow is restricted, the air filter is dirty, or the outdoor unit is not getting enough airflow.
Some common symptoms of a frozen mini split include reduced cooling, ice buildup on the indoor unit, and the compressor cycling on and off. The solution usually involves cleaning or replacing the air filter, clearing any obstructions around the outdoor unit, and potentially having a technician check the refrigerant levels and charge.