Oh - you didn't specify the model and I was going on my 300CD which has two V belts running over the crank/water pump/alternator, with a dedicated belt to the PS pump and another to the A/C compressor.

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'82 300CD
"Pearl", the very first turbo diesel 123 coupe
Totaled 11/23/18, rebuild in progress.
'85 300TD, "Artemis".
'78 300D euro, "Ol' Red", mostly retired.
'85 300D, "Gandalf".