Mythbusters AC vs Windows down.
Saw this on MythBusters
“Last time around, in "AC vs. Windows Down", the MythBusters concluded that using AC was more efficient than opening your windows to cool down. However, they quickly admit that they were wrong to make such a hasty confirmation. In fact, they find that over 50 mph, you're better off your AC on, but slower than that, open your windows. Myth busted.â€