by pilferage » Thu 03 Nov 2005, 01:16:40
An air conditioner is connected to the car's engine (Either by pulley, or via the electrical system.), and when turned on, uses some percentage of the engine's output. So, to go the same distance the engine must use even more energy... And gets slightly worse mileage. The same thing applies to anything else drawing power.
Think of an air conditioner as a backwards engine, it uses energy to change the temperature of air, as opposed to changing the temperature of air to make energy.
I believe the EPA uses atypical driving circumstances because the car's engine hasn't been broken in thoroughly. If they were to test it a few thousand miles later they'd get much better results. For instance, my car supposedly gets 35/45mpg, but I get 45/55mpg. They're pushing the scale in one direction to compensate for the increase in efficiency later in engine life.
"Humankind cannot gain anything without first giving something in return. To obtain, something of equal value must be lost. "