Climate codes old control panel

Hello, colleagues.

For days I have been desperately searching the Internet for a guide to read out the error codes from the control panel of my V8 with first registration 12/89. All the links found lead to the void.

Why I need the codes: my climate compressor "ratters" pretty much and I'm afraid it will break again. Only recently a used compressor was newly installed, throttle and dryer changed, the system re-filled (with replacement for R12). Soon after, the car began to "moan" in right turns. Sounded like a sigh ("pfffff"), which came somewhere right out of the dashboard at the height of the glove compartment. There was no need for steering, because there was nothing to hear when cranking in the stand, even when driving slowly, only when turning right in the city.

So my questions about the error codes:

- can you use the (all) old control panel (only one display) for troubleshooting at all?

- How do you get into readout mode?

- What do the error codes mean?

Thank you in advance.

Bernhard