1991 Mercedes 190e problem with my heater

It is under the dash, in the heater ductwork.

There's a hidden fuse in a small black case directly about 6" toward the front of the car from the visable fuse box. It has a couple of wires going into it. The top pulls off easy and there's a blue 24 amp fuse that controlls the heater. Worked for me! Otherwise to get to the fan itself is 3 to four hours by taking a shroud off by the wiper and then removing the wiper assembly and pop off the back of the black heater box and you'll see the squirrel cage fan. Hot wire it to see if it works. If not may be interrior temp/fan control problems. Good luck