will putting the AC on the lowest setting save gas?

No it will make no difference. The compressor runs the same no matter what you put the AC setting on if you’re referring to the fan speed.

Actually, no it will not. There may be a small difference just because of the amount of voltage the blower takes. When a car is started, the belt is already moving that A/C pulley which is attached to the condenser. Only when that condenser is activated will it create a “drag” on the belt system, causing you to lose fuel mileage just because it takes more horsepower to move the parts at the same speed.

The clear answer is no, the condenser is designed to compress the Freon no matter the setting, even at idle, the only thing that RPM changes is the compression in the condenser.

Mythbusters proved that at a set speed of 55mph, going around a track, the fuel mileage is better with windows down, than with A/C. If going slower, fuel mileage gets better, going faster, it gets worse. This is just because of the wind drag going into the car, creating a high pressure that makes the wind force its way into the car.

AC gas is not something to finish by using it then no consumption in this one at all….

the speed of the fan inside of the cab has no effect on the fuel economy. the fact that the engine is driving the ac compressor is what effects the amount of fuel that is used.

Most drivers will save $ on fuel by the DIY fixes of inflating tires to a hi, but not too hi, pressure [dont forget the spare]; and

Driving @ 55 instead of, say, 75:

“When we increased the Camry’s highway cruising speed from 55 mph to 65, the car’s fuel economy dropped from 40 mpg to 35.

“Speeding up to 75 mph cost the car another 5 mpg.

“One reason is that aerodynamic drag increases exponentially the faster you drive; it simply takes more fuel to power the car through the air.”
http://www.consumerreports.org/cro/cars/tires-auto-parts/car-maintenance/fuel-economy-save-money-on-gas/overview/index.htm