heater problem

[trevorhargreaves]

I have a c250d 1994 it blows hot air all the time and the fan cuts out on no2 speed after a time i have replaced the control pannel on the dash as that was faulty any more ideas before i melt away

 

[sixpack]

Hi Trevor, My C250D (w202) no aircon, just a heater, blows hot air after stopping & restarting with the engine warm.Ive been doing a bit of checking around the 2 water valves (near the fuse box on right of car when sitting in drivers seat). 2 things, 1)they operate upside down,i.e. voltage applied to the valve closes it. 2)the water flow is controlled by varying the on/off ratio of the applied voltage. I disconnected the 3 pin plug on the valve in an attempt to find if the diaphram was leaking, but this only causes the heater to go full on. see 1)above. there is solid 12v Batt on the centre pin of the 3 pin plug, either outside pin should cycle between 0v & 12v at a rate depending on how much heat the controller is asking for. Note that the 2 valves are one for each side of the car. If you take the connector apart, be careful not to short the pins together with the ig. on as this will probably damage the controller or blow a fuse. Hope this is of some help to you.
Peter