Hi, I had the same problem on my 99 Escort, my wife used to keep the AC system on recirculate inside air only, so that it cooled faster. The manual recommended opening the vents to outside when the car is parked overnight so that the air can circulate and prevent mold growth. Any decent auto shop or specialized auto store has the sprays for the AC system treatment. Try NAPPA, they even sell several fragrances. I had the same problem on my 98 V70. One treatment should make the problem disappear and should be enough for one summer. Two treatments are recommended. Regards and good luck.