1985 300 SD CA edition.

I've done a bit more tear down and diagnostic. I do have a small vacuum leak on the "scoop air" control line which I will address. However, the valve itself is working. So far I've been able to verify/correct functionality on the tree of six as well as all the valves sans the above mentioned leaking line.

Unfortunately the answer to most of the above questions is no heat at all. I can feel hot water going to/from the monovalve in the engine bay but there is just nothing coming from the heater core. When I had the interior side panels off I was able to reach my hand into the heater core area through one of the foot vents and it's not even warm to the touch. In all my readings (and mentioned above) I've come to expect buckets of heat as the fail safe but I have nothing.

It is outside temp air which has me wondering if the heater core is plugged (internal/water side or rat's nest in front), something is causing all the air to bypass the core, or something is commanding it off entirely. I'm comfortable enough taking out the CCU and soldering, that shouldn't be an issue. I may just purchase a refurb as the little icons and color wheel are gone/worn. I'll see if the manual has specs to test the thermisters in the air box.

I do have a laser thermometer, i'll see if I can get some readings at different points around the heating system.