I have found that A/C systems are really dirty & gross, and first an air conditioner sucks up dirt, dust & hair to store it in the air duct, you need to get air duct cleaning every 5-7 years… Look up pictures sometimes of seasoned air duct. It will make your skin crawl how gross it looks. The air filter also catches debris from getting into your system. It can only do so much. The inner workings still need a good scrubbing from time to time. There is more than just dust that is a concern as well. The cooling coil in the plan also is a wet place. Where there is wet, mold forms. A lot of people don’t even realize they are blowing air over the mold spores inside their system. It is smart to at least once a year have the unit learn to avoid mold & mildew growth inside of it. Another section is the condensate drain. So much water is flowing here consistently. It is easy for algae to back up & clog the drain. Have you ever seen an air conditioner leaking down the sides, spit out water or be in a puddle of water? This is all due to a condensate drain that is blocked with algae. It is an easy fix, just muck it out. It is really gross but it makes a world of difference. None of the A/C cleaning jobs are hard, just icky. If you are willing to get your hands dirty you only need to call an air conditioner business for service once a year.