Our Panasonic AC units are only 3 years old. We clean the filters whenever the cleaning light goes on. I looked inside and was horrified to see the fan blades as well as the entire interior of the units covered in moist black gunk. Some of it can be wiped out, but the rest would require taking the wall units apart.
Kids have been getting chest coughs and sinus problems monthly and I think this may be why.
Are there professional AC cleaners who will come to your house and thoroughly clean each wall unit and the outside main unit?
This would be for New Taipei City, Sanxia area.