Heater is set on high, heat do not get hot anymore(Warm air) on 1999 Mercedes-Benz CLK430

When slowing down or at a stop,it blows cool air.

Asked by for the 1999 Mercedes-Benz CLK430
poss thermostat or coolant level
3 more answers
Check coolant level, is temp at running temp aprox 180 - 200deg. Water pump would be last option.
When engine is cold, and if you have a expansion tank system, check water at radiator cap. My guess is low coolant too. Could be if you have a bad cap or something is loose on line to expansion tank, coolant will not return to radiator. Also look for a small leak if radiator level is down.
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