Blower K12

So people, After my blower only runs on two levels, already longer, I want to do something against it now slowly. I once googled, but am not much smarter. Sometimes it is said that the culprit is sitting behind the glove compartment, sometimes in the passenger room. Also the photos you see are quite useless. Anyway, as far as I have seen it. K12 ;1.2l; Bj 2007; Limo with three doors. Where exactly is the fan sitting? So the resistance that has to be exchanged. Can anyone give me a tip?