Driving with your windows open increase drag on your car which is often far worse than the energy you consume by using your AC. If you are trying to be more efficient by not using AC and opening the windows instead you might want to research a little deeper into how much energy each consumes :-)

The most efficient way to go is to switch to outside air and let the air thats flowing in cool you down (doesn't increase drag), though, personally, I can't stand the exhausts of all the non-hybrids infront of me.

Rule of thumb - under 45mph roll the windows down - over 45mpg use the AC.

This is a myth, actually disproven on mythbusters! Under controlled track conditions they rode identical vehicles on 1 gallon of gasoline. The car using the A/C ran out of gas many laps before the one with the windows down.

It gets late early out there. - Yogi

Putting FE aside, I thought it was interesting how the ergonomics in the cabin allowed a vortex to develop so precisely. Just give it a try and see what I mean.

Here is the exact information:

http://mythbustersresults.com/episode22

Running a car with air conditioning on is more fuel efficient than running with the windows down. partly confirmed*

Tests were performed under varying conditions (55 mph versus 45 mph). The 55 mph test used a computer to estimate fuel efficiency based on air intake, not actual fuel consumption, and showed A/C was more efficient. The 45 mph test consisted of running the tank until it was empty, and showed open windows were more efficient.

*Because the original tests were inconclusive, this "urban puzzle" was revisited in episode 38:
It is more fuel efficient to use air conditioning when the car is traveling approximately 50mph or more.
Otherwise, windows are more fuel efficient.

My Rule of thumb - under 45mph roll the windows down - over 45mpg use the AC.

Fair enough, though I don't think at mythbusters they tested an NAH which does not run the AC off the ICE but instead its all electric. Also I didn't read anything about what temperatures outside and inside the car these tests were performed at. It may be possible that the AC kept the interior 20 degrees cooler than the exterior temperature while the windows open it would have been the same temperature inside and out, so not a fair comparison

I was wondering about this. If this is the case, all bets are off with regard to any testing of a pulley driven system, I agree. I knew the Pruis had the electric compressor, but I didn't know if the NAH incorporated this. I feel much better about running the AC.

It gets late early out there. - Yogi