The myths of myths...
not a scientific report, (but neither are any of these mpg snippets/factoids tossed around on the web, imo)...
we make several long distance runs per year. From simple observation, I guarantee that I get better mpg,
on average, with the A/C off. This is driving with a window cracked maybe; but I see a couple mpg diff in
either the Vette or the X with A/C on vs. off, on long cruises.
In stop and go, it's no contest: A/C is gonna use more gas.