So I found that w124's use the high side pressure to activate the aux fan. They sometimes have two fans, a engine coolant trigger, and even different speeds but I'm just talking about how the a/c calls for extra cooling. There are 2 different pressure switches one being red and the other green. The red has lower pressures since it's designed for r12 but that's what I'm going to use. On another note, is there a larger drier anyone has tried using? Not larger around but taller. Since I'm going to be using a parallel flow condensor, I like the idea of having more liquid storage...

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83 300CD- sanden, dual p/f condensers, 160a alternator, ect
91 300TD- 722.6, #22 head, 3.5L IP, w140 manifolds, ect