Fact #990, August 14, 2017: Comparison of Vehicle Efficiencies Using the Air Conditioner versus Windows Down

There has been much debate about whether it is more fuel efficient to use the air conditioner or lower the windows on a hot car.

Vehicle Technologies Office

August 14, 2017
minute read time

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There has been much debate about whether it is more fuel efficient to use the air conditioner or lower the windows on a hot car. With the air conditioner running on 50% duty cycle, more fuel was used on a 2009 Toyota Corolla up to 60 mph, but at higher speeds, having the windows down uses more fuel due to increased drag. On a 2009 Ford Explorer SUV, which has different aerodynamics than the Corolla, the air conditioner at 50% duty cycle used more fuel until speeds reached nearly 80 mph. Using the air conditioner at 100% duty cycle in the SUV resulted in greater fuel consumption than having the windows down at all tested speeds.

Fuel Use for Air Conditioner Use versus Windows Down for a 2009 Toyota Corolla and Ford Explorer

Fuel use for air-conditioner versus windows down in a Toyota Corolla. See dataset for additional information.
Fuel use for air-conditioner versus windows down in a Ford Explorer. See dataset for more information.

Note: Tests were performed on a 2009 Toyota Corolla and a 2009 Ford Explorer with three scenarios: 1) all four windows down, 2) all four windows up and air conditioner on 100% duty cycle, and 3) all four windows up and air conditioner off. Results were then modeled for a fourth scenario of the air conditioner at 50% duty cycle. Both vehicles were gasoline and were tested at steady-state speeds.

Source: Huff, S., West, B., and Thomas, J., "Effects of Air Conditioner Use on Real-World Fuel Economy," SAE International Journal of Passenger Cars Mech. Syst., 2013, doi: 10.4271/2013-01-0551.

Fact #990 Dataset

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