For some time I've been getting a musty, mildey odor when I open the external vents or turn the heater to the defrost setting. It is worse in cold or wet weather. I have a 2002 WRX Sedan.

Rick

 

I forget the details, but my dealer told me that Subarus have the tendency to get that. It is actually mildew. Just go in to any Subaru dealer and they can spray some chemical in your vent system to kill it.

 

I've read this somewhere, do you think this may work?

Open the doors wide (not while driving), turn the fan on it's highest speed, select fresh air on the dash, turn on the A/C, then using a spray can of Lysol or equivalent, and spray it into the vents on the outside of the car, near the base of the windshield. This will pull the Lysol intothe vents and coat the areas where the mildew collects / breeds. Continue to run the fan for a while, as the Lysol in concentration can be a bit tough to breathe. It will clear out, and the mildew should be gone.

 

Um, yeah. Or you could just go to the dealer and they can do it for you.

 

Yes, that is one way to deal with it. There are also other products on the market besides Lysol that are specifically made for this purpose, parts stores and dealer parts depts. may have them.
I would not run the AC when doing this though, you don't want to introduce more moisture into the evaporator which is what the AC does (why the mildew develops in the first place). Just run the fan in vent mode.
Also if you have the inside cabin filter take it out before spraying, or whatever you spray will get caught in the filter and won't get to the evaporator. In fact, you can also spray directly into the filter housing (with the filter out), this will give a more direct path to the evaporator.
In the future, to avoid the mildew problem don't use the recirculate mode unless absolutely necessary, keep the vent on the fresh air setting. Also, don't keep the AC running right up until the car is shut off- at least a few blocks before reaching your destination, turn the compressor off but keep the vent fan running. This will allow the water in the evaporator core a chance to drain and allow it to dry out, so there won't be any standing water in there to promote mildew growth.