Quote Originally Posted by niky View Post
For older cars and cars with smaller engines, the drag of the AC compressor is greater... leading to higher fuel consumption with the AC on (heck, with Nissan Sentras with the Calsonic compressor, it could rob a ton of horsepower). For bigger-engined vehicles, it seems like less of a problem... but setting the AC to the lowest comfortable setting (highest temperature at lowest fan speed that still feels cool from all seats) is always a good idea...
Highest temperature? Or you mean cooler setting with low fan speed?

You have a point either way, but for optimum fuel economy, the higher the temperature setting, the less work the compressor has to do. The colder the desired setting, the more work the compressor has to do. More work leads to more fuel consumed.