Quote:
Originally Posted by Richard Wooldridge
I suspect that your auxiliary water pump is not working. The mono/duo valves need to have the pressure that the auxiliary water pump produces to make the valves work properly. when the car is idling at a stop light, there's not much pressure from the engine water pump, so the valves cannot stay closed. When the car runs at a higher engine rpm, the valves start closing again. The solution is to replace the auxiliary water pump, or change to a different type of valve. I drew up a drawing of the change I made on my '82 380SL, which had the same problem. It's on one of the diesel threads, if you have trouble finding it I can probably look it up.
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Richard,
I will check your change later today.
I already called the workshop (the car is there) asking them to test fuse/aux water pump.
This site is all about synergy: take a look to at the text below, pasted from another article by S. Brotherton, from the site referred by Terry.
While it says you may be true it also warns that the control module may be dying...
Thanks for your support, Jorge
"HEATER WATER VALVE
The last factor involved in Mercedes-Benz climate control is the heater water valve. From simple vacuum-controlled, on/off water valves to multiple pulse width-controlled water valves, each model can be different. Early models used auxiliary water pumps to help when temperatures got too cold. Systems starting with the 124 chassis have used the auxiliary water pump to maintain a uniform heater core temperature. Failure of this pump causes a couple of nasty problems. The first one is straightforward, if you catch it before it damages more than one pushbutton controller. The pump locks and the current flow burns out the controller — a good thing to check out if you are replacing the controller.
The second problem caused by the pump (or lack of pump) is more subtle.
It shows itself as sporadic, sudden bursts of hot air, which are produced when a car that is mixing heat and cold to achieve control sits at a light. Due to a no pump and poor engine flow condition attributed to the slow speed, the water valve is opened to full to try and raise the heater core temp. When the car starts moving, the water flow grows rapidly and the heater core goes full hot before the valve can control it.