The heating, ventilation and AC (HVAC) heater box is susceptible to mildew buildup. This can result in a musty odor from the HVAC system, most noticeable when the system is first turned on.Google+
Car Problem Reports
Mercedes-Benz C240 Mildew in Heater Box
Mercedes-Benz C240 Problem
Average Mileage: 72,552 mi (40,000 mi - 90,000 mi)
Mercedes-Benz HVAC are the worst in the world. The Windows constantly fog up, blower goes from zero to full-tilt with one tiny notch up on the knob. Always too hot or too cold in the winter. In the summer, you can't use the A/C because it smell like a Nazi concentration camp. Took it to MB stealership, got charged thousands as they told me what was wrong, nothing changed (as in improved ANY of the problems I described) and the and the smell is somehow even worse now. Service "salespeople" say that they cannot "duplicate the complaint" while my family are in their bathroom barking ours guts out from the stench.