I have the clinate control manual for the w201 of that year. The 190. The systems must be similiar. There should be a valve that pulses heat into the heater box. I would check if the lines to the heater box are hot. If they are then it is problem the blend flap vacuum pod. Find the vacuum seitches. On the 190 they are accessed from passenger side under dash panel. Pull vacuum and see if they hold. If they dont, then the pod diagphram is bad. This is a guess from my 190 experiance.