In the heating mode, warm air will occasionally be emitted from the movable nozzles (1)

Who thought that would be a good idea? It makes absolutely no sense "hey you're driving in the cold, so how about we don't blow hot air out of the center vents" I'll never understand... I thought it was broken for the longest time after rebuilding the climate computer, then I eventually read that in my manual.

I digress... From left to right you have:
Defrost - full heat and full AC at the same time with full blower. Gives you warm dry air to the windshield. No recirculate.

Bilev (what an american car would call it) - defrost vents, dash vents, and floor vents.

same as bilev, but no defrost vents. American cars might call this "Max A/C".

Same as above but economy mode, no A/C.

Fan control in auto gives you speeds 2 through 4 automatically. Bottom button is speed 1, top button is speed 5.

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1984 300TD -- summer daily driver
Many others that aren't Mercedes...