Did a test today to see how much fuel economy is hit by turning on the A/C. Answer: a lot, 2-3 mpg typically. It depends somewhat on how fast you are going, whether you are on flat ground or on an incline etc. Out where I live I notice that when you press the AUTO button and the climate system does its magic, sometimes the A/C is on and sometimes it is not, even on a 50 or 60 degree day. How does the system know what to do, especially when it is not actually hot out or hot inside the car? Where I live temps in the summer are cool and I rarely need A/C at all. Now I know to make sure it is off unless I actually need it, especially with premium gas at $4/gal.

 

I set my system on auto at 76F year around. I never change it, just let it do it's thing and keep me at perfect temperature regardless of the climate. Same with the rear A/C. The rear UV disinficts the air which was good for the Covid mess.

 

Totally worth whatever it costs here in Phoenix

 

That is weird, I have never noticed more than a 1MPG drop on mine measuring at the tank, even running it all the time. It caught my attention in how efficient it was because I was used to a 2-3MPG drop with other cars I've driven. I keep mine set to 75 though, that may have something to do with it. The climate system in these cars is amazing though, it regulates the temperature beautifully and always feels comfortable inside, no matter what it's like outside.

 

I think the mpg hit might be due to the engine just loafing along and needing little fuel to maintain speed on flat ground due to aerodynamics, the AC load is significant (10% increase, roughly). The climate control system on this car is awesome. I'm just a little too obsessed with fuel economy.

Running without AC on a cool summer day, hilly terrain, speeds 45-65 mph, country roads. Would have topped 30 if I didn't get stuck in traffic having to wait for a bridge to open.