I think I may have figured out my problem! When I went to Toronto is was snowing and crappy out so I had my front defrost on the whole time. On the way back it was nice out so I did NOT have it on. I read in my manual that the a/c compressor comes on in every position but floor and vent. Which means when I am driving my car with the defrost on ALL THE TIME I am getting bad millage because of the a/c. Make sense???