Procedure to check AC Push Button-Fan Switch
 

Someone please help me!

Car:
W201
190e 2.3L
4 Cylinder
1988

I am in a third world nation and need serious help in diagnosting the AC system. Long story short, the comprossor comes on but the fan blower does not work. I have verified that ignition switch is not the problem. What I have been told is that it is either the Push Button Control Panel or the Blowter Switch Control in the dash. (Blower Motor Workd whe I hook up direct power to it)

Could someone here help me and post the procedure to test these? Other than just swithcing out parts? Parts on this here are expensive and hard to get therefore, I would like to narrow it down. Is there a way to check the voltage and so forth or hooking wires to see where the fault lies?

Thanks, Ignacio