Sounds like the relay is dead. Open the cap on the klima and ask somebody to look at it while you turn on ac. You should see it move. Also try manually pressing the contactor with your finger and closing it. Something is obviously happening. I think you may have a big contact resistance on the relay.

Ooh…or the controller is burned and not throwing the relay when the pressure switch closes. I think that’s how the klima works. I recall it takes a bunch of inputs like throttle switch, rpm, pressure switch etc. to close the compressor relay. It isn’t like the old school w123s that kind of wired everything in a daisy chain.

The transistor tilted up looks like sloppy assembly. These old boards were hand loaded then wave soldered by humans in Germany. I’m a little stunned the part was crooked but it seemed soldered in correctly.

I’m not familiar with the diode on the plugs. Are these devices to keep the inductive spike from destroying the relay? Looking at your board both relays are protected by flyback diodes on the board.

You may have to trace the wire back. But as I said if you are seeing a small change on the compressor voltage that likely means the relay is burned. It’s like a huge resistor right in series with your compressor. You may need to grind the contacts a bit. At the end of the day the clutch is just seeing a relay switch closure to 12v. The relay is either on or off so if it only goes to 42-52mv that screams burned contact. If you shot enough current through to melt the board you may have melted the relay contact too. Likely your switch (relay) is the weak link.

I forgot if I mentioned it before but I simply wired my own relay in place of the klima. There are a number of posts here on how to do it. It doesn’t perfectly replicate the klima function but when I hit the ac button my cold comes on. All it takes is a lamp relay and some wire. I broke my old klima board out of the box and reused the old pin contacts and black plastic enclosure. Nobody knows by looking at the outside that the whole thing is hot wired.

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