First off It was not a fuse!
In front passenger side underneath the glove compartment.
A blue box with an aluminium case attached to it. Its a Resistance
for reducing volts.
What caused the problem:
In order to turn the 12 volts into 3 volts (to drive the fan etc.) the resistance part gets very hot.
The cable/wire going into the resistance had melted due to overheating.
The socket which is made of plastic was melted and caused the a disconnection of wire and metal part of the resistance. When disconnected the fan would not receive any power.
How to fix:
Underneath the glove compartment there is a cover with fabric. Remove this (no unscrewing needed). In the top left corner the resistance is located and fastened with two screws.
After we unscrew everything and unplugged one of the two cables, the other would NOT unplug no matter what we did, we realized it had melted together so we had to cut the remaining wires to get the whole thing out. Only than we could remove the melted part. After we cleaned the melted part and the cable we reattach the wire together again with melted tin and a rubber membrane to protect, also from touching each other.
Tips. Get a very good flash light, if need be (as in my case) gently remove the blue top of the box with a screwdriver to flip it off (no screws).
a happy AO