Querying the air conditioner for errors

Hello.

Querying the air conditioner for errors: Can someone tell me which
The channel for the climate is exactly accessible. how to detect errors?

(My old problem 20 min. Everything is cool, then nothing goes and so much more - the more the climate heats - what else can be to blame here, I had everything exchanged...?)
Today I was still with Audi: Nice problem but no idea what this could be..
Tomorrow there's some kind of Luefter Relay, which I'm sure it's not.

Many greetings
Bernd