The answer to 'why is my ductless system not cooling' is that there are several common causes, including low refrigerant levels, a malfunctioning compressor, blocked airflow, or a problem with the thermostat or control system. Symptoms may include the system running constantly but not cooling effectively, warm air coming from the vents, or the compressor not kicking on.
If the system is low on refrigerant, you may need to have a professional HVAC technician recharge the refrigerant. A compressor issue or electrical problem will likely require professional repair. Blocked airflow from a dirty air filter or obstructed indoor or outdoor units can also prevent proper cooling, which is something a homeowner can typically address themselves.