So, while doing some experimenting on where best to put my Pex valve replacement in my '81 300D, I discovered some information while looking at the Service Manual, and thought I'd pass it on here.

If you are wanting Fresh Air Only (No AC or heat), here's the settings:

Wheel set to MIN---EC button pushed in---Fan set to AUTOM

What I noticed with that today, is that after about 10 seconds, you hear the fan kick on, then after about 20, the fan kicked in to the 5th of 6 settings and stayed there. More importantly...NO ADDITIONAL HEAT FROM DEF OR CENTER DUCTS! Air was basically ambient. This is not a bad way to go if your AC is non-functional; at least you get a flow of air when at a stop sign. I tested this today on a 90 degree day; my fingers felt no additional heat from the ducts other than the ambient heat from outside. Handy to know, in my opinion!


Now, if you are wanting to completely CLOSE your system off from either the monovalve, AC or fresh air; here's those settings:

Wheel set to 22---O button pushed in---Fan set to AUTOM

That setting apparently closes the monovalve, turns off AC, main air flap is closed, blower is not running and recirculating pump is not running. What I noticed in this test was, indeed, NO AIRFLOW OR HEAT OF ANY KIND OUT OF ANY DUCT! Another awesome thing to know!

You will have to try this out for yourself. May explain why some of us get heat in the cabin for no apparent reason in the summer. While you'd think the simple OFF "O" button would shut everything off, it's apparent to me that's not the case.