The smell you are getting is due to the condensation on the evap core. When the A/C is running, condensation builds up if there is high humidity outside. You get a mildew smell because when you shut off the vehicle, the condensation sits on the outside of the core and grows mildew like you get in your shower. There are a few different ways to fix this, the spray mentioned above, any kind of household spray like Lysol will work to. The fix from your dealer will be a re-program of the BCM to run the fan for a few mins after shutdown or instalation of a device called an after blow module which will run the fan after shutdown. You can do the same as the after blow mod by turning the temp to full heat for about 1 min. before you shut off the vehicle, it will cause the condensation to dry on the evap core. I used to work for Delphi Harrison at the Service technology group bldg. at the GM Tech center in MI and we studied many different ways to solve this problem. It really only happens in hot humid climates during the summer...
