Not sure if this helps or not:
https://charm.li/Mercedes%20Benz/2010/C%20300%204MATIC%20%28204.081%29%20V6-3.0L%20%28272.948%29/Repair%20and%20Diagnosis/Heating%20and%20Air%20Conditioning/Heater%20Core/Service%20and%20Repair/