A3 1.6 FSI - Fans stick on

[a31.6fsi]

I seem to have a problem with the air con. Sometime but not all the time my fans stick on and th temp gage bottoms out (causing massive fuel consumption)
I got her plugged into a comp and the guy said i either needed a temperature switch or a temperature sensor, to which my dad got me but no one knows where it goes and only suggests putting it into an Audi garage.
As you can appreicate i dont want to go to that expense, could anyone explain where this goes in my car (jan 2004 A3 1.6 fsi) and also if this in fact will solve the problem. I've also noticed the car is a bit jittery and bit revy first thing when the fans are stuck on (maybe not related)

[A3_FSI_2.0]

not 100% sure but as a guide, there is a coolant temperture sensor on the block of the engine that tells the ecu what temp the engine is to adjust the fuelling. There is also one on the radiator lower hose that controls the fan that keeps the radiator at the correct temperture. Not sure if this controls the aircon fan too but I'm guessing it does. IIRC I read about somebody having a wiring issue there that burnt the fan out.