[slotard]

Yeah, at 20mpg I could see a 3mpg drop from AC... at 9mpg that's a TON of extra fuel. For a 100mi trip, 20 to 17 means you burn (100/17 - 100/20) = .88 gallons extra. 9 to 6 means you burn (100/6 - 100/9) = 5.6 gallons extra.