We discussed this in depth on the w116 forum, so I figured I would copy the details to BenzWorld as well!
Over the past couple months, my friend in Stuttgart, Germany and I developed a replacement kit for the pesky Chrysler automatic servo and amplifier. We used a modern printed circuit board with a microcontroller to take the inputs from the car's sensor chain and convert those signals to control the heat and a/c. It functions the exact same as a functioning servo would, and doesn't alter the interior control panel.
The installation process is very similar to replacing the servo. My board plugs in place of the servo wiring harness, and then you make a couple vacuum connections. Additionally, a few wires are jumped across the harness connector inside the glovebox to bypass the amplifier. A vacuum-controlled heater valve goes between the aux. pump and heater core to regulate water flow.
Unlike other products on the market, mine was not developed with the idea of mass production + profit. This allowed us to use much higher quality parts. For example, the electric solenoid motors inside my kit that route vacuum to control the heater valves and internal vent valves are medical-grade solenoids made by ASCO industries with a rated life of hundreds of millions of cycles.
My apologies if I come off as a salesman to anyone
I owned a 300SD, and now own a 380SL; they both had the pesky automatic system. Developing my own solution was more practical than paying for another kit or rebuilt servos.
They are about half the cost of a new servo. Anyone who's interested let me know! They just hit the market.
Any suggestions + ideas regarding the kit and system, in general, are greatly appreciated!