A/C Usage and Impact on FE

[fowljesse]

I grew up in Arizona, and had crappy cars most of the time. I got used to the heat, sort of. I had a '66 Buick Skylark that had an Iron block V8 with Aluminum heads... Not good in 100+ degrees. After the 1st time I heard the "Tink" of the metals expanding at different rates, I started running the heater in rush hour traffic. I sat in about 170 degree heat for about an hour, 5 days a week. I usually had a headache, and was nauzious when I finally got home.
Now I have A/C, and it doesn't affect my car much (about 240HP/ 2400lb. car), and I never use it, just out of habit, and ridiculous FE interest.