The German automobile club (ADAC)
needed another 0.2 l/100 km (less than 1 mpg) with the windows open, between 80 and 100 km/h. Using the A/C to modestly cool the car from 28 deg C to 22 was 2 to 10 times more costly in town.
Their test vehicles were a Ford Fiesta 1.4, a Mazda 6 2.0 MZR, an Opel Vectra 2.2, an Audi A4 1.8 T and an Audi A4 2.0 TDI. Using the AC was between