Hi,
My wife and I just drove from Huntsville to Nashville and back at 65-70
mph with AC. The trip mileage came in just about 49-50 MPG with the AC (I wasn't working on accuracy, just trying to get her to an appointment.) At ordinary cruising speeds of 65
mph, I would expect about 53-54 MPG. But consider this, the EPA highway rating (old style,) was only 45 MPG and they used a slower average speed, 48
mph, without AC.
AC isn't free but it sure is affordable . . . and makes the wife much happier.
Bob Wilson