Mercedes-Benz W212 heater not heating
The W212 heater does not heat even though the engine is warm. What is wrong?
One cause is a blocked heater core. Silicate from the expansion tank (an additive that reduces cavitation) can get into circulation with the coolant and clog the core. In that case the core and the expansion tank are replaced. The blockage can also cause weak heat on only one side.
Why does the W212 blow cold air from only one vent or only on one side?
The cause can be a fault in the footwell vent temperature sensor or damage to its connector or wire. The sensor is located in the kick panel, and changing the fresh air filter can break it. The roof unit temperature sensor can also give wrong readings and confuse the temperature control.
Why does the W212 automatic climate control not blow warm air right after starting?
With automatic climate control, the blower only starts once the engine temperature is about 60 °C, and strengthens after that. With a cold engine, the lack of airflow is therefore normal.