Originally Posted by Lucky13
I wonder how much impact running the air conditioner has because I have always gotten better mileage in winter months when I rarely use the air except to remove humidity like on rainy days. I typically get 1-2 mpg better in winter, keep in mind that in summer when its 96-100 every day and humid here in SC my air conditioning is getting a major workout.
I would expect it to be significant. According to a study from 2007 called "Reduction in Vehicle Temperatures and Fuel Use from Cabin, Ventilation, Solar-Reflective Paint and New Solar-Reflective Glazing", about 5.5% of all the fuel used in light-duty vehicles goes to the interior cooling systems.
I would expect that figure to be much higher in the South, and lower in the North.
(The heaters we run during winter don't use nearly as much energy - in part because they steal excess heat from the engine that's generated anyhow.)
Combined with likely not getting the inferior winter blend gas, I'm not at all surprised if you get far better mileage during winter, while we who live closer to the poles get far better mileage during summer.