Switch on the A/C @ Fan speed 1 and note down the time when it gets tripped.
Now do the same @ Fan speed 2, 3 and 4 and note down the time. You'll notice that @ speed 1 it gets tripped frequently i.e. after short duration of time and it gets increased according to fan speed.
In Old cars like Corolla 86 OR suzuki khyber there is a seperate button of "Economy" and while using that .. A/C gets tripped more frequently as compare to A/C button. and in those models.. Fan speed doesn't make any difference...
So fan speed in new models does effect the fuel economy.