My stinky a/c

I would go to the parts department at a Toyota dealer and buy a charcoal cabin filter. It will cost a little more than a regular filter but it might help. I put one in my Avalon and so far I have no problems. Last year when I was using the regular cabin filter I was getting a musty smell but so far it has not returned since I put the charcoal filter in.

 

dealer has a special system for cleaning the a/c. along with oki's advice above, start shutting your a/c off a few minutes before parking, and run your fan high to dry the system out so mold doesn't grow.
and baking soda on the cabin filter if the charcoal doesn't do the job.

 

The guys on NPR's CarTalk swear by this stuff.

There are other places to buy it. I actually used a competing product that was half the price and it worked fine.

Bought the Interdynamics stuff at the local NAPA auto parts store.

Replacing cabin filter is probably a good idea, but I would not bother paying the extra for the carbon. Treat the ducts. Let it run a day or so and then put in a new cabin filter.

 

Just use the same system the dealer uses. It works great I do it once a year. My dealer stopped selling me the kit over the parts counter but thanks to a poster here found another can that works just as good.

The dealer uses a 2 can kit one spray can is a compressed microbial cleaner with a special hose interface attachment that attaches to the ac condensate drip tube under the car. Connect the hose of the can to that drip hose and push the can button and it empty's its foamy soapy contents into the e coil under the dash as foam. Then quickly comes back out as liquid. The dealer 2 part is another can of horrible old lady perfume they spray in the windshield air dam while the ac is on. It really stinks the cabin up. Its so there customers when they get in the car feel they got something for there $125. Cleaner is enough for me as its very pleasant.
The foamy cleaner can I use is a Kool It on Amazon.com

Then while your at it go to Home Depot and buy spray AC Coil Cleaner. Buy 2 cans. In the engine compartment take off the black plastic valence cover over the radiator to get a view of the front condenser. Spray that condenser down with the AC Coil Cleaner. Hose it good with the cleaner. You can let it sit and then rinse it off or it will rinse itself. Try to gently clean off the bugs too. Maybe with a hose. Same thing you should be doing to your home outside ac unit.

You will be rewarded with much colder ac. The hard part at home is jacking the car up high enough to get to the drip tube under the car for the e-tube maiantencae. Its right behind the passenger front wheel about a foot and a half in up on the body. It comes down just to the left of the glove compartment. The tube is only 2 inches long so hard to get to and head to find.

If diy is impossible then get the dealer to do it and pass on the perfume can. Btw, this is a modern car malady not so much a Prius malady.

Good Luck. You'll love your car again.