....
Econ = Economy
If you sit at traffic lights and switch the AirCon on and off you'll hear and see the engine revs change and therefore more fuel is being used.
Just cruising in town or similar, I'll have the sunshine roof open on days like today and have my rear windows down just an inch to release the cabin pressure.
I don't like the road noise of open windows either but I only use the AirCon (heater set to Lo) to chill the cabin in short periods.