Chrysler Repair: smell in 98 Chrystler T&C, chrystler, sour milk

Question
We have a sour milk/dog poop smell coming from our vents.  You can smell it outside of the car too.  I seems to only occur in the winter and it will go away sometimes so it isn't contant.  It does not go away when you adjust the heat for location of air flow or with the A/C on.  Can you help me?  1998 T&C.  

Answer
If your air is not working well it is possible that your evaporater is leaking and that will cause an odor.Or you may just have a debris build up or even mold on your evaporater.All of these conditions would be a reason to replace the evaporater.There are companys out there that do a cleaning service but they don't really work.Evaporater replacement is an expensive job and the dash board will need to be removed.Mind you I am not able to smell the car.