I almost never run my A/C anymore, but when I did, I only noticed about a 2-3 mpg (10%) decrease.
At this point, I've mostly weened myself off of using the A/C. We've had a pretty mild year, and in addition, my car is white and most often parked in the shade. I'm thinking I might get a UV reflective tint at some point, but I haven't really needed it yet.
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