We've had a few A/C threads lately. What I haven't seen--though I could have missed it--is a description of how A/C works in the Prius, and what the most energy-efficient way of using it is. OK, OK, I know from the discussion and life generally that Prius A/C works like most other A/C in the world, with a compressor and a cooling fluid. I also figure that you use more energy the cooler you try to get the car. The questions that I'm asking are these: Is it most energy-efficient just to turn the thing onto Auto and let the computers decide how to cool it? Or, as I suspect, is it more efficient to turn the fan down a bit from the full blast you get on Auto and cool the car more slowly, if you can stand it? The reason I suspect this is that in Eco mode the fan doesn't run as fast as in Normal. When the A/C is not on Auto, is the system still trying to cool the cabin to your target temperature? If not, what's it trying to do? When the fan is on High, is the compressor working harder, or just the fan? And if I've asked too many questions, is there any place to go to get the whole story of how the Prius climate control system works and how to use it best? BTW, Little Rock, Ark, hit the highest temperature ever recorded here, 114 F yesterday. For GrumpyCabbie, Socrates, and all the other non-USers, that's 45C.