Is the MPG boost with summer gas completely cancelled by A/C

I don't think so. Some of my best mpg tanks were in the hot summer, around 95F outside with the ac turned to about 70 inside the car. My car will get alot better mpg in 100 degree weather than it can in 30 degree weather, and i'm going to use the ac heavly to make it feel good inside the car.

I didn't respond to your questions right so i need to edit it. But what i'm trying to say is i didn't notice ac doing much to my mpg, i kinda think it helps the traction battery to feel the cold ac, rather than it getting to hot and not being able to be used much.

 

I live in Mississippi, which has mild winters and humid summers, I see MPGs near 42 in both summer and winter, while spring and fall are about 47 MPG. I tinted the glass to the amount MS law allows to improve summer MPG, next winter I try grill blocking.

 

I'm gonna say it depends upon your driving - at freeway speeds, A/C won't have much effect - if you are in stop and go, it will cause the ICE to run more often to charge the battery - if you are doing short trips in hot weather, it really kills your mpg because it takes extra energy each time to get the car cooled down.

I get the best mileage in the spring and fall when the weather is not too cold or too hot.

 

If you don't have the A/C at 50 degrees (e.g. 75ish) and leave it at auto then you'll probably not see too much of a difference. Personally, I never have. The time temperature murders my MPG is when it goes down to freezing or below.