I had a W126 Benz (1981 280SE) on which the heater would not turn off on one side of the car (it has separate heaters for each side). The problem turned out to be a broken solenoid valve in the heater water supply. The way the heater works is: With the ignition off the heater valve springs open. When the ignition is turned on the heater valve automatically closes. When you then turn on the heater controls the valve opens again. I think the idea is that the heater valve gets "cycled" every time the car is used so that it doesn't get sticky. The electric solenoid that does the closing is easy to find by following the water pipes and will probably be on the firewall somewhere. They are supposed to be a throwaway part but I got mine open and soldered up the broken wire and all was good.
The heater on a Mercedes c200 will stop working if the heater core is blocked. It allows hot coolant from the engine to be used in heating the cabin.
It may have a bad heater core.
You need to change your thermostat in the car.
Most likely a replacement heater core
this is not an answer just an update. coolant is filled
It is because your heater is having to heat up so its blowing cold air out while its heating up.This means your heater is not very efficient and it needs to be checked.
check your coolant level. if its full, might be a plugged heater core.
is the blower motor running? or is it just not blowing hot air?
Is it not hot? Not blowing? Leaking coolant? Need more info to help you.
Check the temperature control cable
heater core plugged or air locked check to see if hoses going to heater core are hot
to heat a space. the ducts move from the evaporator(a/c) to the heater core, where the core has hot antifreeze going thru it and a blower motor blowing across it produces heat