A number of posters have suggested turning off the AC to improve mpg. As it's an engine-driven accessory, leaving it off will increase mpg - but we need to know how much. So I have a request for anyone out there with a scangauge to run this test and report:

1) On the highway with cruise control on, run the AC for at least 10 minutes (so the temp can stabilize). Then, on a level stretch of road, note the instantaneous mpg reading off the scanguage.

2) Turn the AC off. Then note the mpg increase on the scanguage and report it here

 

FYI - Edmunds conducted their own test that's related to your question.

Test #4 A/C On, Windows Up vs. A/C Off, Windows Down

Result: Nice in theory; not true in practice

Cold Hard Facts: No measurable difference (unless you open the sunroof, too!)

Recommendation: Please, make yourself comfortable.

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