You have it reversed. Unless you're like in warm tropical window-fogging situation (like summer rain in FL or something) you want to bring in fresh air instead of having A/C fight the continual battle of removing YOUR moisture from the air (breathing, skin).Make sure you're on recirculate to get the moisture out of the air
This - fresh air/AC is the magic and when it's raining out/humid even when cold I always run my AC in the winter for de-fogging. Also reduces the number of "why does my AC smell like ass" posts in the spring!Assuming there are no coolant leaks in your heater core and any free water is wiped up, give this a try. Works every time for me. Should be cold outside for this.
1. Make sure recirculate is OFF
2. Turn off the A/C
3. Crank the heat to high, make sure the car interior is really hot, may need a while to heat up. Go for a long drive.
4. once all warmed up and driving, lower the windows and exchange the warm moist air for cold dry air. Do this a couple times.
5. enjoy your frost free car.
The A/C works well to quickly defrost in the winter but the moisture seems to get trapped and expelled when you stop the car and causes a re-frosting. The above works for me. Once it's done rarely need to re-do the procedure unless we get rain.