OK, I've read *extensively* some of the old threads on V-belts and I think I understand where I got stuck now...
My Mercedes factory manual apparently gives the wrong procedure for tightening the A/C compressor belt (you can also see the image provided by TooMany MBZ, which is an exact copy of my manual page for that job).
The manual gives an oversimplified procedure for the A/C compressor belt:
"1) Loosen fastening screw.
2) Tension V-belt by swivelling tensioning roller [MIND you, this is at the idler pulley, NOT the A/C compressor...The factory manual does not mention messing with the A/C compressor at all in order to tighten that belt]
3) Tighten fastening screw."
The several posts I've read on this just now say otherwise...they say all the A/C compressor bolts need to be loosened along with the metal clamp holding the freon lines and then play with the adjusting strap in order to tension this belt, and nowhere do they mention to do anything to the tensioning roller (idler pulley) which is the only focus of the factory manual for this job. Here's the best explanation I've found, by vstech:
Changing Belts 240d
Loosening the tensioning roller (idler pulley) bolt worked perfectly to free the belt.....but I was right when I saw no easy way to do the reverse procedure for tensioning it.
So, I'll try this approach tomorrow early morning. If someone has some experience with the york compressor and thinks there are additional things I should know working on this, please contribute your knowledge here.
Tomorrow I'll also use PB Blaster on the tensioning mechanism for the alternator belt....after completely loosening the three bolts....let's see if this leads to a different outcome.
Any thoughts/advice/suggestion you might have please contribute here. I'll read whatever was posted tomorrow morning before attempting these tasks again.
God bless...
EDIT: Actually that procedure from the manual is perfect for my 1979 240D with York A/C compressor. I was able to use an adjustable wrench on the rectangular structure on which the idler pulley is bolted and tension the belt that way while tightening the fastening bolt behind the idler pulley with my other hand.