The combustion engine charges the high-voltage battery and the 12-volt battery, as well as propels the car too. The car gets 40+ MPG overall, but the combustion engine alone only performs at a max of 20 MPG because it's energy is also used for charging the other batteries.
The more that I run the a/c in the car, the less MPG I get because the engine is spending more energy recharging the batteries (and consuming more gasoline), because they drain faster with the a/c on than when the a/c is off. That means that less gasoline is being devoted to propulsion.
In jets, especially during times of high fuel prices, what I read was that running the heaters for creature comfort used more fuel than running the heaters at minimum comfort levels until someone complained. I guess the question is whether the extra fuel consumption is noticeable or negligible.
-PJ
Given your frame of reference, I understand where you are coming from with your question. But I can unequivocally tell you that there are much greater factors affecting fuel consumption other than cabin temperature setting. By far, an aircraft’s change in altitude is going to affect fuel flow because of the variance in air density and therefore the fuel/air ratio.
I have a three hour flight tomorrow from Texas to the eastern Caribbean. I’ll put your theory to the test with extreme but brief changes in the selected cabin temperature. Hey, I can’t tick off the boss’s family sitting in the back now, can I?