Ventillation fan problem

There is a power transistor for the fan. If you only have high speed that is almost always the cause. I don't recall where it is located on a 328 but on the TR and Mond it is in the air duct just behind the cabin air outlet. It has to be located somewhere in the air ducting to keep it cool. It has 3 large wires, I think red, white and black or yellow. The wires will come out a hole in the air duct so that should help you find it. When the transistor goes it also takes the small fuse located in the fan speed controller with it.