haha did anyone watch this on mythbusters last year where they prove this with two brand new 04 expeditions.. the one with the ac on and windows up drive 15 miles less on 5 gallons of gas then the one with all the windows down and AC off... so it was proven on national TV that driving on the highway with windows down and AC off is better then with it on all do to yes there is wind drag but once the mass is moving it makes little difference. the engine still pulls at he same rate not to mention the F150's have vent windows to let the air flow freely through the cab. for me on highway i can get 18-19 with AC on and loaded down with friends junk... while moving out of his appt. and with ac off and windows down i get 20-21 depending on outside temp and speed.

 

In addition to the drag argument, I would add that the parasitic loss from the compressor is insignificant compared to dragging around 5,000 pounds through the air; rather un-aerodynamic; starts; stops, wind, how spirited you feel that day, etc.

 

On the same subject, does anyone know whether having a bigger engine affects the amount of fuel economy lost with a/c on? It would seem to me that if you have a 5.4L, it wouldn't have to work as hard as a 4.6L to drive the a/c resulting in less difference in gas mileage. Am I right, or an idiot?

 

Episode 22: Boom-Lift Catapult
Buster lends a hand as the MythBusters explore the myth of the boom-lift catapult. Will Buster overcome the raw power of a 30,000-pound piece of machinery, or will the boom-lift turn into the ultimate medieval catapult? Then, worried about the price of gas? Tune in to Jamie and Adam's investigation into the most fuel-efficient way to keep cool in the car: turning on the air conditioning or opening the windows.
premiere: Nov. 10, 2004

i'll see if i can find the results i saw the show know the results. they used 5 gallons of gast per vehicle and its a half mile track they went around the expediton with the AC off and all windows down went 30 more laps then the expedition with ac on.. both were 5.4L 3v engines

 

hmmm, I thought ac on won on mythbusters...

 

Well it hit 105 here today. Hell with the milage. I bought a truck after all so I'll use the AC when I want to.

 

nope there was a whole 3 mpg difference since he was able to drive 15 more miles on 5 gallons of gas then the expedition with the AC on