Just figured I'd share my solution to this problem as many people seem to have it and there wasn't too much definitive info out there, just a bunch of bits and pieces everywhere.
Whenever i would run my AC or defroster in my car, I got a musty/moldy smell. You become immune to it after a while but everyone who rides in my car notices. Dealership just gave me the usual answer of replacing the cabin air filter. I tried this but it did not solve my issue.
After some research, it seemed that the issue was due to mold in my AC evaporator and/or in the hoses for it. I went to NAPA and bought some A/C Pro Auto Air Conditioning Evaporator Odor Eliminator (UPC: 048168025671). It was about $10. It is a foaming cleaner in an aerosol can with a cap/tube attachment. I also purchased a new cabin air filter since youre supposed to replace it when using the AC Evap Cleaner.
The cleaner is simple, spray it through the AC Evap drain tube til it starts to foam back out the end of the tube. There are 2 ways to access the drain tube, from under the car or under the carpeting on the passenger side.
If you access it from underneath the car, you will need to lift the car up to be able to reach the drain tube. it is located almost directly underneath where the shifter is, slightly off to the passenger side. Insert the hose for the cleaner as far as possible and spray it up into there,
I chose to access it from inside the car where it comes through the firewall. To get to it, you need to go thru the passenger side front door. Pull down the carpeting paneling stuff along the side of the center console, starting from the front of the car to the end of the first piece of carpeting. It is pretty easy to pop back into place as it bends so don't worry. There will be a black rubber hose behind there (its the only hose there). You have to roll back the rubber hose from the front to the back after removing the 2 little rubber tabs on the hose. Insert the hose for the foaming cleaner into the part going into the firewall as far as possible and spray the cleaner through. Quickly slide the hose back over the end and re-secure it, you wont need to access this again so you can close it all up while the cleaner sits.
Then you let it sit for about 15 mins (it will begin to drain out the AC evap drain tube out onto the ground almost immediately, so if you don't want it all over your garage floor use a bucket or do it outside!). Then you let your fan run on the lowest setting for 5 minutes (I let it run for 25 mins after that with the system on full blast after that and doors open to get rid of the smell of the cleaner, but it int a bad smell at all).
The final step is to replace your cabin air filter. Open the glove box. There are four screws around the glove box holding it in. After undoing those screws, you can pull the whole glove box assembly right out. Be careful though, there is a light attached to the top of the glove box you need to unplug before you completely remove the glove box. The filter is right there behind a rectangular panel that just unclips and drops down.
I would also recommend having your local dealership turn on the after blower feature on your car if you have this issue, it'll help stop the build up of condensation causing the mold. It just runs the blower fan for a few mins after you turn off your car to dry out the AC Evap. I hope this helps, wish all this was in one thread when I was trying to do mine! I had a faint smell of cleaner for the first day or two. But its been over a month and no more bad smells, just cool air!
