Thanks ap0gee!!. Thanks also to dragman, whose phtograps made clear some aspects of the process (I don't understand slovenian, it's a pity :P).
I finally fixed my Fabia Combi air con this morning, after three hot hot summers (Madrid, Spain, you know...). You, ap0gee, can do what Skoda service couldn't (they charged me 250 euros for what they called a "servo").
I found two small problems: the damned ECU bracket and sensor's position. It was easier than I thought, after all. Here is a picture of the place and position where you can find it, right up the accelerator pedal (my steering wheel is at left). I found easier access by arranging the seat on an horizontal position and lying upwars over it.