Hey Guys-
I am copying this thread that I posted on the 380SL forum. I recently owned a 1980 300SD with the ACCII system, and now own a 1981 380SL with the same climate control system. Both had failed Chrysler servos, so I made this replacement kit:
I'm starting a new thread regarding the climate control servo replacement I developed with my coworker/ friend in Stuttgart, Germany.
As you probably know, the first gen climate control system uses an amplifier to control a very complicated servo under the hood. The servo/ amp controls four main functions: letting water into the heater core, controlling the fan speed based on the user inputs, and opening the leg and center vents based on user inputs of hot/ cold/ defrost.
The servo failed in my car, and I thought Unwired Tool's price of $600-800 was ridiculous based on my knowledge of electronics and what parts make up their replacement kit.
Thus, I reached out to my friend in Germany and we developed our own using Mercedes and Chrysler documentation from the when the system was designed.
To install my unit is very simple. You remove the amplifier + servo and install a few bypass wires in the wiring harness (of the amp), a w201 chassis heater valve, and a tube in place of the return line from the servo. It took me about two hours moving slowly

My board plugs directly into the wiring harness that went into the servo. The microcontroller then receives the user inputs from the temperature selector wheel and sensors inside the car.
Additionally, my board uses three vacuum solenoid valves to accomplish the same goals of the old servo: 1) Controls Hot Water 2) Controls Leg Vents 3) Controls Center Vents. A circuit made up of four relays directs fan speed.
The vacuum lines from the servo connector plug into the three different solenoids, and one vacuum line plugs into a source (such as the reservoir). Thus, based on user controls, my software on the board tells each solenoid when to open or close, and also directs the relays. This replicates the original function of the cumbersome servo and amp.
I can sell my unit a lot cheaper than the OEM servo or Unwired Tools. Additionally, since it uses modern electronics there is no expensive risk of failure, as associated with the servo.
It will take about two weeks to manufacture for anyone interested. I’ll sell the whole kit with the w201 valve, vacuum lines, board, etc for $325 to anyone interested. I also plan to write up a little instruction manual and take some photos of the install on my car. You can PM me if you want to hear more/ get a kit! Thanks a bunch.
-Davis