Any test procedures on this? Voltage pin-outs, etc.?

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Figured it out. Pulled the amp and re-soldered the traces and components on the circuit board.

I'll try to post a pic of the bad solder joints. Electricity and electrical components are NOT German strong points!



The lines are leading to solder joints which were actually loose. You could wiggle them around in their sockets. Notice the darkened areas on the PCB. That is from poor connections leading to increased resistance/heat. Spent about an hour touching up ALL the solder joints, replaced the board and voila`! A/C working as it is supposed to now. Vents open and close, blower speed changes according to temperature readings, compressor cycles, etc.

NOT a job for the average week-ender. Requires a steady hand and a small soldering pencil. I used a 12 watt I have from my electronics repair days. Some of those traces are CLOSE together and it would be only too easy to create a bridge if you are not extremely careful.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

What year is your W123? I have the Electrical Troubleshooting Manual for the 107 from 1983-89, which covers ACC generation III. Unfortunately most of the schematics for the ACC unit are block diagrams.

There is a separate manual that covers the system in detail. While this link connects you to a source for the R107 ACC, it may likely cover the same ground or you may be able to find a source for a specific year of the W123.

Mercedes Benz 107 Climate Control Heat AC Air Condition Manuals

Then there's the Encyclopedia Germanica Volume 107, here:

https://www.benzworld.org/threads/the-encyclopaedia-germanica-volume-107-aka-egv107.1450550/

Scroll down to the section on ACC. There are a variety of articles on problems and repairs. Yes, it's for the 107, but I suspect all of MB's ACC units are the same or similar enough.

1978 ACC version II. Vertical buttons. Problem solved with re-soldering.

I was hoping to find a pin-out diagram to check for faults without removing the amp.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now