My Mercedes 190E's HVAC system still works great... most of the time. Every now and then, the blower quits blowing and a high pitch buzzing emits from the blower speed switch. The only way I can remedy the situation is by turning the ignition off. When I switch it back on, everything returns to normal. I have replaced the blower motor, blower speed switch and several fuses, but as of yet, have not found the silver bullet. Any help would be greatly appreciated.

 

I have finally solved this mystery! After replacing nearly every component in the HVAC system, I found that the ignition switch (electrical) was defective. It worked well enough to start the engine, but the supply current to the switched accessories was poor. It was strong enough to run dash lights, gauges, etc. but not enough amperage to power hogs like the blower motor and its switch. The relay within the switch would "buzz" in a futile attempt to energize the blower motor. Once the ignition switch was renewed, a daunting job in itself, everthing worked perfectly. So my beloved 190E rolls on!

 

To locate the blower control resistor, windshield wiper then plastic panels under windshield wiper must be removed. Then remove wiper motor and linkage assembly. In the center of the car under the wiper linkage the plastice heater motor cover must be removed. Remove heater motor. The resistor/controller mounts directly below the heater motor. Resistor unit and wire harness must be removed as an assembly. Install new resistor and work back through directions. Due to the amount of labor involved it is recommended to check the blower motor at the same time.