These are not ordinary A/C smells. Burned refrigerant has a chlorine, mettalic smell, but not rotten eggs. This is suspiciously similar to the smell that drain cleaner has eaten through a p-trap and the sewer gas is passing through the duct.
Someone needs to look at the plumbing stack near the air conditioner blower condensate line to see if there is a water seal to prevent stack gases from being sucked into the blower. Also inspect the return ductwork where plumbing drain-waste lines pass to look for holes in the duct and/or the plumbing.