I have the exact problem with my 91 300d 2.5

I was in the car when this happend, fan motor fine (no noise) that I changed from auto to high, and no fan and none of the buttons worked. Later I restarted the car and everything worked fine. the other buttons work fine the ac comp comes on and off. Then nothing, the fan will not work at all with any of the 3 buttons. Everything else works fine. Where is the blower regulator???