This article is from the Chrysler-Plymouth-Dodge FAQ, by Dr. David Zatz with numerous contributions by others.
David Ta believes the a/c smell comes from condensation collecting on the
horizontal fins of compressors used on some models. One way to prevent this
is to blow hot air for a couple of minutes before turning off the ignition.
There is a Chrysler extra warranty of 7/70 on LH evaporators).
This is a problem on many different makes and models, and normally the
dealer will try to solve it using fungicide. David Ta also said a GM friend
of his mixed water and baking soda, and poured it into the drain area next
to the firewall, later rinsing with a water hose. He did this once a year
when he winterized.
A new solution (sent by David Ta) was described by Popular Mechanics, in
November 1996: AC Delco's kit No. 15-8632 and relay (if necessary) 15-8264,
to run the blower for 5 minutes, an hour after the ignition is turned off
if the a/c has been turned on for at least 4 minutes. The article also
gives a short-term fix with GM spray can and verifying the evap drain hole
at the firewall is not blocked.