We all seem to be saying the same thing- heavy AC use kills mpg, and for the only hot/humid climate member who actually drives with and without AC in the summer- it is the same 4 mpg hit the hot/humid members have noticed( medstudent- no AC-Houston summer???-Yikes!!)
The folks who don't notice a summer drop-Seattle,S CA,Illinois,Seattle,Chicago- don't live in brutal summer climates, so they can tolerate moderate AC use(they think they live in hot places, but a trip to Phoenix-hell on earth-would change their minds).
Phoenix, New Orleans,Georgetown TX all notice the drop.
Houston has tried it both ways.He/She is demented, but very helpful(thanks MS) Luck,Charlie

 

somoene mentioned in another thread that over 100F or so the battery starts to protect itself. You may have to turn the ac on at that point. Just set it to 99 or whatever the battery needs to come out of protetion.

 

My mileage has dropped to around 42-43 with A/C on essentially all the time now.

Before the Texas roasting season set in, I was doing 48-50, so that works out to 6-7 MPG to stay cool.

It's a hoot though to have the A/C keep going with the engine Auto-stopped. When I pick up my wife after work, I leave the car auto-stopped (gear shift in neutral) at her office until she comes out. The engine will stay off for about ten mins, which does pull the battery down several notches, but then again, she rarely needs ten minutes to finish up and come out.

In the past, I never let a car sit running and burn fuel just to have the A/C on, so this is just one more neat capability of the Hybrid!