Everyone believes that using one’s car airconditioner consumes more fuel, but the startling result of a controlled research has got us all wrong. On the other hand these guys are saying: “To save fuel, use your airconditioner!” Alarming as it is, it is true and scientifically proven.
Three same-model cars were selected for the test. They were to cover the same distance, x, in the same time, y, and therefore at the same velocity, v. All external variables were made as constant as possible for all three cars so that the results would not be ambiguous or misleading.
Car A was to make the trip with the glasses up, the AC turned on
Car B was to make the trip with the glasses up and the AC turned off
Car C was to make the trip with the glasses down, and the AC turned off

REPORT:
It was discovered that Car C had consumed more fuel than Cars A and B, both of which appeared to have burned an equal amount of fuel. Several theories were proposed to explain the puzzle, the most scientifically-compelling of which was that the air resistance was highest for Car C which had to do more work, which meant burning more fuel in order to overcome the negative force exerted by the air against which it moved. Cars A and B with their glasses up did not bother much with this negative force and therefore did not burn the extra fuel.
So, based on the authority of these reports, “Save fuel: turn on your airconditioner!” is insightful wisdom, ironical though it sounds.