Thanks so much for the helpful tips.
I never notice if my car's heater is working (as HK is too warm).
But for sure that the fan doesn't work no matter the "colder" knob is on or off. And I also noticed that the blower switch is not riveted to the lever-assembly. It's attached to it by 2 pins.

I agree it's wise to learn more from the wiring diagram, but where can I get one? And website provide such info?
Pls advise if anyone knows.
Many many thanks!

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'74 W114 230.6
'87 W201 190E 2.3-16
'97 W210 E320 Avantgarde