I looked in the FSM on startekinfo.com in the climate control section to try and find a table of acceptable factory pressures as intended by MB but can't find a table.

I'm looking for something that shows acceptable high and low port pressures based upon ambient temperature and humidity. I assume such a table will also have acceptable vent temperatures.

Is it in some other part of the books? I have to assume this info was published by MB?

Oh wait. I found it but it only has readings for the 110, 116 and 117 engines. The 1986 supplement does not have the graphs. Ill keep looking. Must be here somewhere

Well. For anyone who wants to find it Look in the W124 manual. the M103 engine is the W124.0/2 diagram

Pressures should be pretty close to the same on any system, as pressure is directly related to temp. A wise old dealer mechanic told me that the only way to get a proper charge in any automotive system is to fill it from a full vacuum by weight. Unlike a big commercial or even home HVAC, an automobile AC has a very small quantity of refrigerant. Adjusting by pressure is not nearly accurate enough to avoid under or overcharging by a few ounces, which is a pretty significant amount in such a small system. Unless you are seeing a real difference in pressures (blockage in the expansion valve or such), best to not adjust unless it is bad low or high, overall. If you have to evacuate, fill to specified quantity by weight and go.

In your 2nd gen W126, you'll never see a vent temperature lower than ~40-41˚, even with a perfectly functioning A/C. There's a sensor on the evaporator that cuts off the compressor around that point to keep the coil from frosting. On a HOT day, once the car has cooled down inside, you should be seeing somewhere around 45˚ at the center vent when moving, around 48-50˚ when idle.

A P/T table is only good if you're running R12 with the original expansion valve and an unclogged filter/drier. If your car has been converted to R134a or any of the "alternative" refrigerants, forget about going by the book.

__________________
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Yup, there are tables for conversions from R12 to R134a, pressures, weight of charge, etc... All kinds of stuff online, just google.