87 190D Heat/AC

[jgauto]

I've been working on the Climate Control on my 87 190D for a couple of months of and on. I had some vacuum leaks and I replaced a vacuum valve behind the instrument cluster and one behind the center console. The push button unit also was replaced, it was melted inside. After replacing all of the above, there was still heat at all times coming from the outside vents and defroster area. I did one last adjustment on the potentiomter (sp.??) and the system started to work and cut off the the heat to the outside vents. The next morning the system was back with heat. I checked the potentiometer adjustments and changed it to 2.7 volts and the system once again began to work properly. The next day heat is again present at the outside vents. The A/C only comes from the center vents. Any clue/direction on this matter???

Check the vacuum line to your heater control valve at the right of the battery under the windshield grille. If there is no vacuum applied the valve will stay oopen allowing coolant to flow into the heater core. Also, heat is not supposed to come from the center vent only sides, floor and windshield as determined by your dash buttons.

[mbdoc]

What vacuum reading do you have at the switchover valve assembly(when cold)? Maybe the vacuum pump is weak, common on this car until engine warms up!!

I've not taken a reading but can feel the vacuum on the hose and when it is disconnected the valve opens to allow coolant to flow. The name I heard is the heater control valve which is in place of the monovalve on my vehicle.