“If it was the AC compressor loading the engine then it’s a different story”
The affects on gas mileage when using AC in a fine tuned automobile is negligable. Maybe 2 miles to the gallon. I know, I watched Mythbusters blow this theory up> :)
It is true though. It is a myth that excessive fuel is used while running the AC. Down here in Tejas, the AC is a necessity in the summer, if you don’t want to sweat your @alls off. I don’t lose mileage like some think one might. I still get 420 miles to a tank, with our without AC
Did they test the difference when sitting still? You wouldn’t get a lot of gain from reduced drag from having the windows up if you’re not moving.