Ok. Last summer I stayed in Savannah for the most part. I put a thermometer in my car just out of curisioty, and every time I got in the car it would be maxed out which is at over 140 degrees F.
That means most of the interior peices are that temperature, and trust me when you're already hot before you get in the car, rolling down the windows isn't going to do any good at all.
Actually if you want to be comfortable you have to have the AC on for a while before you get into the car.
I usually start making sure my AC is in good working order in April or May.