Thanx, JamesDean. I may have to take you up on that. Kinda (rots) that the AC seems to work, but I can't access it!
As I found a Temperatureregler (sp?) way up under the dash on the right side, I am guessing the SD system you took the pictures of is similar to the system I have (a D)?
Just to verify, the most common failure would be bad solder joints / loose components ? If so, I will check one set, and leave one set unmolested to ship your direction if I fail to detect and fix the problem. (I am nowhere near your level of expertise, but I am not completely over my head as far as soldering components. If it is obviously broke, fine. If it is any component much past a resister, I don't have the test gear to check.)
As far as the blower fan speeds, it appears to have several. I have a resistor box on the fenderwell, I thought that was my fan speed control (corrections cheerfully accepted).
2 more questions, and please chime in if I am wrong in my assumptions!
1) I will have to verify whether the aux pump works (currently not operating, but if it isn't getting power from left plug pins 10 and 12, it wouldn't, will try feeding it direct)
2) how critical is the foam pipe to the dash sensor to system operation?

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1984 300 D runs, interior
1984 300 D light hit in front, RUST, mint/perfect dash, decent interior (see above), parts car
(hate to kill one)
1998 Dodge diesel