If a hacker can do all that, why can't the car itself open the windows slightly if the temperature inside gets high and there is no rain outside?
It's safer to just put a solar panel on the roof, my car has it integrated into the sunroof. When the interior temperature rises sufficiently and the panel is sunlit then it runs the blower motor to keep the car cool. Sadly, it ignores the ambient temperature sensor and has no concept of humidity, so in some conditions the sun can hit your car, heat it up before the surroundings, and suck damp cold air into the vehicle and humidify it. In the normal course of the day, though, it will blow warm air through after it, and the air at least comes through the cabin air filters.