What are the economics (at least in terms of fuel efficiency) between driving with the air conditioner on and driving with “360 A/C” (i.e., with the windows rolled down)? Air conditioning draws on power, which reduces mileage. Windows open increase drag, which reduces mileage. 

Not surprisingly, there’s no easy answer (it varies wildly with the vehicle in question, the temp, the speed, etc.), but the simple rule of thumb seems to be that a/c is better at freeway speeds, windows at slower than that.

Now, which will keep you cooler (vs. more solvent) is another matter.