jonta_dj

I've got a problem with the air intake (or whatever it's called) on the right side of my 87 w124.

Look at the pic below, on the left side (circled with red) when I turn up the heat I get warm air coming from that side, but not from the right side (circled in blue). Why is that? What can I do? This is a european model, and it doesn't have AC and stuff, just something that "mixes" the cold and warm air I guess.

dlafever

Is sounds like the water valve for the right side is not opening when you turn up the heat, perhaps a broken adjuster or a sticking/blocked valve?

bamberger_1

It has to do with the so called dou valve in front of the battery. It opens the circuits for left and right heating circiuts. To check the valve just unplug the the 3-prong plug and then both side should get warm air. If this is the case the valve seems ok, since it is opening when no voltage is applied to the two circuits. In this case it is most probably the heating control unit which transmits wrong signals to the valve to open or close. The mixture is done by the duo valve opening and closing for certain times, depending on the outside temp. and the inside temp. Another problem, but not as likely is that the right sensor for the temp. delivers wrong values to the conrol unit. The sensors can be checked by taking out the control unit and pull the electric plug and measure the sensor's resistances. You would need the diagram to take measurements. The resistor values are: @ 10C 18,2-21,5 Ohm; @20C 11,5 -13,5 Ohm; @30C 7,5-8,5 Ohm. The sensors measure the inside temp. and the temperature at the heat exchanger right and left.
I had the same thing last year and after trying everything I swapped the control unit with one from the junkyard (€5) and eversince then its ok.