Why home air conditioner stinks?

The coils gather dust and make water (condensate) which feeds mold. Change your furnace filter after you spray the coils down with a weak bleach solution. Use a wet-dry vac to pull the wet dust out of the coils. Be gentle with the coils because folding the fins over will reduce the efficiency of the AC. You will usually find the coils in the furnace plenum. Cleaning the coils will improve the efficiency of the system and remove the source of the stink.