I had an issue with the fans on my Passat, I ended up telling them how to fix it.
The sensor that tells the fans to come on is actually built into the fans and is not a serviceable item, the fans need to be replaced to fix it.
What the receptionist said to me about it still makes me cringe to this day and prompted a call to the service manager ASAP to ask in no uncertain terms what the hell was going on down there. They are a long standing 'specialist' VW garage.