Do note that the battery system draws its cooling air from the passenger cabin. If the cabin is too warm for the average hairless ape then it may be too warm for the battery also. When a battery and its controls are too warm they have to throttle themselves, limiting the charge and disharge rates. It may actually be better for MPGs to use the AC.
Richard makes a good point. The battery system is cooled from cabin air, so if it's way too hot in there, the battery could be throttled to prevent overheating. I always make the following recommendations for the hot summer months. These are universal for all cars. (adapted for the Prius here) Get your windows tinted! It really helps. Get a shade for your front windshield. It really helps. Use it religiously. It has a secondary benefit of keeping harmful rays off of your dash and other parts of the car. Crack a window. Hot air needs to be able to escape the cabin. Park in the shade where you can. When starting a drive, roll down the windows to let the hot air in the cabin vent out. Leave them open for a minute or two once you start moving. Turn the AC on and set it to vent/fresh air. Run it on fresh until the cabin air is cooler than the outside air. Roll up the windows when the AC has cooled down enough. After a few minutes, turn on recirculate so that the AC is only working to cool down the cabin air, which should now be cooler than the outside air. With the Prius, at this point, edge the temperature setting up until you are no longer comfortable. One or two degrees lower should be the optimum setting for you.
Tint the windows! We did our Subaru with black leather interior and it made a huge difference. We have done the Prius with some cheap DIY stuff. It cuts down the heat gain dramatically. We also use a silver windshield cover while parked,, as we usually travel with the dog. Icarus
Yes, but be aware that when you park under a tree, you may get little droplets of sap all over the car. Recirc is more efficient, but the lack of fresh air on a long trip can be a problem. I get sleepy without a steady supply of fresh air, which could explain why I feel truly alive only when exercising outdoors.
Don't dial a high temp (i.e. 80F) into auto setting ... could hurt your FE on a cool morning. see this ... http://priuschat.com/forums/gen-ii-...emed-reduce-fuel-economy-auto-turned-off.html
Setting the climate control to 80F causes the engine coolant to flow and heat up the heater core... Thus warming up the air... and cooling down the engine... Thus forcing the engine to run all the time to generate heat...