What is stale moldy smell coming from inside air vents also no water drainage un on 2010 Chevrolet Malibu

No ac water dtains out under car after ac use.

Asked by for the 2010 Chevrolet Malibu
I had a bad smell in my Malibu the first year when I had the air vents open, no air condition or heat was on. I contacted the Dealership and they said to spray a can of Lysol into the air vents and then turn the car on and turn the air vents on high and let them run for 20 to 30 minutes. I did this a couple times and the smell finally left and I haven't had a problem since. They said something in there is plastic and it will have a smell. Unreal!