300e w124 No heat when I stop.
 

My 1989 300e blows heat only when I'm driving down the road. The faster I drive, the more heat I get. When stopped, the blower motor runs fine, but instead of heat I get cold air. Is there a second fan somewhere that isn't working?

Thanks,

Bill

300e w124 No heat when I stop.
 

I would start with your mono valve, it sounds like it's not letting low pressure coolant through it to the heater core.

300e w124 No heat when I stop.
 

There is an electrical circulationpump on these models. This pump helps to circulate the water to the heater when the engine is running on idle. Your pump is probably standing still, had the same problem on my -89 300E.