Heres one for you. My 1998 E320 4matic 's cabin heats properly after starting and warming up. It warms to the set temp. then the heat shuts off. Outside air then comes through the ducts. Heat only returns if the control is set to Hi. Any ideas? Thanks so much! Chas.

 

Hi,
Your symptoms don't signal a fault.
Once the car is up to temperature the climate control decides the cabin is too hot (the driver and the sun act as a heat source into the cabin) and lets some cooling air in to stabalise the temp at the set temperature.
Moving the setting to Hi calls for more heat so the cool air stops and more heat is delivered.
Stuart

 

Thanks, but the heat doesn't come back on by itself. It will stay off until --well until you restart the car, or turn the heat to hi.