I read a few similar topics on the forum. I will briefly describe the heating problem in my car (Mercedes w202 c-class 94r 2.5 Diesel):
On the left side (from the driver's side) warm air is constantly flowing. It doesn't matter if I set the left knob to min (cold) or max (warm). Reading topics on the forum of people who had a similar problem, I started to check what could be the cause. At the beginning, the simplest method "on the bulb" - that is, I connected the bulb with cables under the plug that connects to the pins that are next to the solenoid valves. So, as I marked in the picture, the left solenoid valve (right side of the passenger heating) turns out to be operational. The MIN (cold) light bulb was on when I turned it to MAX (hot) - it went out, so the voltage from the control panel is working properly. However, when checking the left side of the driver (pin of the right solenoid valve), the bulb did not respond at all. Did I turn the dial to MIN or MAX. Wogle was not sending a voltage signal. So I figured something was wrong with the heating control panel.
My questions are as follows:
Can I get around it by connecting PINs 1 and 3 together ?? (marked on the photo) Where is MASS ?? Can it cause a short circuit? The signal goes to PIN No. 3 (GROUND), but not to PIN 1. So can they be combined together ?? The mass of the left solenoid valve to the mass of the right? I got this idea because it seems to be the simplest solution to this problem. So it will turn out that the right knob will control both the heating side from the driver and passenger and the left one, broken, will not perform any function ??
I would like to ask for help as it is getting warmer and I would like to do something about it and fix it myself.
Most likely, the overload protection will trip and turn off the current. This is what, for example, W124 from that period - the type of heating is very similar. Incidentally, this could also be the cause of the fault. Just in case, compare the resistances of both coils. I guess it's supposed to be 14 ohms - but that's a quote from memory