Roll Down the Windows
Manual air conditioning systems can be even harder on your fuel economy. The AC consumes more gasoline in city driving than on open roads. Since you're not traveling fast in urban areas, simply rolling down a window can provide a breeze without the fuel penalty. However, on highways, using the AC is the better option. Opening windows at high speeds creates drag, slowing the car and increasing fuel consumption. It's a choice between two evils, but for highway driving, the AC is the lesser one. Ultimately, your car's air conditioner is a fuel guzzler that hurts both your vehicle's efficiency and your wallet.
