FM is right on. 5 minutes from destination, turn off AC, put on fresh air, not recirculate and run fan on medium through all vents.
Blower box has a drain in it, if clogged water builds up and smells or gets mold. If you can get to the blower motor you can take it out, get 3' of soft hose, the clear kind you can get at a hardware store, put one end int the box then slowly pour water into it. If water runs right out under the car, the the drain hose is most likely not clogged. Do not poke or jam anything in there, if you damage the heater core that is a major repair cost.
The problem is usually in the evaporator housing under the dash. The evaporator becomes wet with condensation in use and does not dry itself in most cars. Mold grows and the smell begins.
Auto A/C shops can clean the evaporator housing with professional grade foam treatments for a modest cost. Keeping it from happening again is mainly a matter of running the fan with the A/C off for a few minutes when you are shutting down the car.
More than likely the heater / air conditioner duct-work is infected with bacteria. The dealer of the car or truck can spray a disinfectant in the air entry duct at the base of the windshield with the heater blower motor on to pull the disinfectant through all the duct-work to kill the bacteria.
Read this on how to get rid of mold on the evaporator coil
http://ricksfreeautorepairadvice.com/ac-...
Make/Model/Year is Nissan/Xterra/2007
