We've been in this house 5 years, and it occurs to me (since the AC seemed to stop working yesterday and now, mysteriously, works again today) that we have never done anything except change the air filter a couple times. Should we be doing more? Like, having a professional do something? Can't they vacuum all the cheerios out the ducts? Or do we just carry on with our current course, which is to pretty much let it go unless it stops working?