Perhaps it depends on the climate and the level of comfort that you require. In sunny So. California, A/C is required in the summer and an option that I occasionally used in spring. I believe that we have experienced a 3 to 5 MPG hit from summer time use of A/C in spite of a change to more economical summer-blend gas. So far, the weather has been in the high double digits, with triple digits expected. During this first summer with our Prius, we have set the A/C at 74-76 degrees F, depending on whether there is direct sun exposure on occupants. The A/C has been on during virtually all of our summer daytime driving.
Well DUH!!!!! the lower the temperature, the colder the air.. just joking...wasn't trying to be an A$$
MSantos had a AC suggestion: when starting off with parked car that has a hot interior, use Auto (let the car determine fan speed) and set the target temperature high enough that the blower fan doesn't race. This might mean setting the temperature around 28~30 degrees centegrade. As the car cools lower the target temperature, staying below the threshold where the fan really starts to race. Try to stabilize on a temperature just cool enough for comfort.
