I forgot you had a KLIMA in your 85 but I don't believe that affects the mono-valve, just the AC. You really need to get your hands on a wiring diagram for your specific car so you can troubleshoot. Hopefully, someone here has the diagram.

Let me ask a basic question, does the heat seem to work normally? If the heat is working (adjusting the temperature based on the setting), the mono-valve and it's controls are probably OK.

When you select AC, do you get hot air, or just outside temperature?