Air-conditioning in cars means that you have both heating and cooling systems in the cabin air feed.
There is no separate magic "drying" system. It's the cooling that does the drying. Warm air can hold a lot more moisture than cool air, so on a wet spring day, cooling the incoming air gets a lot of moisture out, which condenses on the cooler matrix then drops out underneath the car. That leaves you with cool air, but it's still saturated with moisture. You can then warm it up again to get your required cabin temperature, which means it can hold a lot more moisture, i.e. it's dry, and demists the screen much faster.
If the outside air is already cold then there isn't a lot of point in trying to cool it down further. Just heating it up will dry it out.