The answer to 'mini split smells bad' is that a foul odor coming from a mini split air conditioning system is often caused by mold or mildew buildup in the unit. This can happen when the system isn't properly maintained or cleaned regularly. The smell may be musty, rotten, or even like sewage.
Some common causes of mini split odors include clogged air filters, standing water in the condensate drain, or bacterial growth in the coils and ducts. Neglecting routine maintenance like cleaning the filters and draining the condensate can allow mold and mildew to thrive, leading to unpleasant smells.