a/c & gas
simple answer is yes. Can decrease it is as much a 4 mpg highway mileage on avg.
Wrong. Ok if you have your windows down at or above 45 miles an hour it creates too much drag causing your MPG to decrease. So 45/+ windows up ac on, 45/- windows down.
If you are adding the wind/drag coefficient, it may be the less of the two evils, although I do not believe the person asking the question was comparing the two. The use of the ac compressor draws power from the engine, therefore reducing power, increasing fuel consumption. So-------- if it is wintertime and you are not using the ac you get better gas mileage then you do in the summer when using the ac windows up or down. I believe it was a simple question.
Your right Michael, very simple question and its a very simple person that could argue with your answer.