How to switch the fuel saving mode of Audi a4?

I read the explanation about the economic mode switching, but I don't understand. In addition, under what circumstances should it be opened? Yes, even if the light is on, it is still on. Questioner: Feng's best answer: When the light is on, the light is on. This button represents that the switching of air conditioning economy mode has nothing to do with driving. Just press this button and you can run in the most fuel-efficient mode. Pressing this button for heating in winter makes no difference, and pressing this button for cooling in summer is obviously different. Although it saves fuel, the temperature can't drop. ECON is equivalent to the empty adjustment of compressor switch!