The windshield defroster can also be used to cool the interior of the car, although not as much as the air conditioner. Using the air conditioner reduces fuel economy, does using the defroster do the same?
When the defroster is on, the AC compressor is running. Therefore, there's no savings by trying to cool your car with the defroster. Leave the climate control in Auto A/C and adjust the comfort level by adjusting the temperature. I leave mine there year round.
Selecting Defroster will keep the A/C compressor running (regardless of your previous setting or whether the A/C light is on or off).
Using the defrost setting to cool the car would use more fuel because the cooled air would be heated by flowing past the glass.
