The answer to 'mini split smells bad' is that a foul odor coming from your mini split air conditioner is usually caused by mold, mildew, or bacteria buildup in the system. This can happen when the unit is not cleaned and maintained properly. Symptoms may include a musty, rotten, or sewer-like smell coming from the indoor or outdoor unit.
The best solution is to have a professional HVAC technician inspect and clean the mini split system. They can access hard-to-reach areas, disinfect the coils and drainage system, and make any necessary repairs. Homeowners can also try some DIY maintenance like regularly cleaning the air filters, wiping down the unit, and using a disinfecting spray, but more thorough cleaning is usually required to fully eliminate the odor.