What do you mean put another valve upstream? I tried clamping the heater supply hose, but the clamp started to cut into the rubber before it could tighten the hose enough.

The default position for the valve is to be open, and when the valve is "energized" (from the Benz manual), it becomes closed. I think that means that when the electromagnet is on, the valve is closed, but I'm not sure.

I'd love to fix what's wrong with the ACC, but I don't know where to look next. I don't know what shorted when I touched those 2 wires together that go to the monovalve, and I don't know why the monovalve wasn't working properly before. I was hoping someone here had some ideas.

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Gabriel
'91 350SD 162k
'83 300SD 210k - rear-ended and scrapped
'84 300SD 210k - totalled