If your car’s AC isn’t working properly, you have two choices on how to drive down the interstate on a hot day. We’ve now tried them both.
Option 1: Ride with the windows up and the vents blasting. Riding with the windows up will increase your gas mileage, though it will also make the car a rolling greenhouse. The blasting vents will, theoretically, blow over the sweat forming over every inch of your body thereby cooling you. We did not find this to be the case. Instead we ended up hot, sweaty, sick, and probably irritable.
Option 2: Ignore the better gas mileage and drive with the windows down. The air is much cooler blowing by you at 70 mph. The only other negative effect is that your ear will ring a little from all the wind.
Don’t be that person who has to find out for himself. Take my word that option 2 is much better.