With the cost of gasoline as a concern for many, tips abound on how to help a car achieve its maximum gas mileage. One fuel efficiency concern that has been tested and debated hotly is whether the air conditioning on a car decreases fuel efficiency. Some argue that the air conditioning unit causes a drag on the engine, causing it to burn more fuel. Others argue rolling down a car's windows causes an even larger drag on the engine.
The air conditioning's compressor is powered by a belt on a pulley system, just like the alternator on a vehicle. The engine is what turns the pulley system, so in other words the engine powers the car's air conditioning. Running the air conditioning in the car does create a drag on the engine, making it work harder. Anything that causes a car's engine to work harder decreases the engine's fuel efficiency. In other words, if you do not need air conditioning; going without will save gas.
Driving with a car's windows down does not create a drag on the engine. Having the windows down to catch a cool breeze decreases a car's aerodynamics, however, which means the engine has to work more to maintain the same speed. The aerodynamic drag from having a car's windows down increases as the speed of the car increases, says Stanford University's School of Earth Sciences.
The amount of the effect of an air conditioner on a car's gas mileage has been tested and debated by several organizations. The Society of Automotive Engineers, or SAE, performed a series of tests on the effects of air conditioning versus windows rolled down on sedans and SUVs. The SAE concluded running air conditioning in a car or SUV decreased gas mileage by 5 to 10 percent, depending on the vehicle model. The SAE, Stanford University, and Bankrate.com all recommend driving with your car's windows down if you are on surface streets. When it is time to get on the highway, though, all three organizations agree using air conditioning is the more fuel efficient choice.
