Yeah, no A/C in 100°. Silly, eh? I'd been exercising and was overheated and the dry breeze felt good.

As far as A/C versus no A/C ...

I remember the TV show "Mythbusters" tried to test this a couple years ago. They started with a computer model showing aero drag should be more than compressor drag. But then for some reason they could only do the test at 50 MPH. At those speeds A/C used measurably more fuel. No surprise there, since wind drag from windows isn't much of a factor at 50 and A/C is a factor at and speed above zero.

One of the car mags did a better test, but it was years ago and I only remember two things from it: At highway speed A/C was technically best but the advantage varied by car. Under 60, both compressor drag and windows-open aero drag were measurable but so small as to be considered a non-factor. They basically said to use A/C on the interstate but otherwise to do whatever makes you comfortable, since the MPG loss at lower speeds was not worth sweating over.