1996 Dodge Grand Caravan "SMELLS" when turn A/C on

Hello all. Our 1996 Van with 110,000 miles, 3.3 engine Automatic Transmission, all the bells and whistles has developed a "STINKY-SMELL" when-ever we turn on the A/C. We were told there is not any CABIN-FILTER that needs to be changed. Any IDEAS?? We APPRECIATE THE HELP!! Thank-YOU!! My wife is an athsmatic and we need to resolve this. The local Dodge dealer has been of no help. Again, Thank-You!! dooski--