AC Repair: Troubleshooting Common Air Conditioner Problems

I have an error in the control unit.
(Vehicle: Leon 1M, Engine: ARL, 1.9L, 150 hp, Year: 2004)

18065 Air conditioning unit - Input/Output - Short circuit to positive.

What could that be? / Where could that be?
Unfortunately, I don't know where to look for that information, and I don't have any wiring diagrams.
Gibt es da einen Stecker der vielleicht einen Wackelkontakt haben könnte? If so, where?

The car doesn't have any other issues, and the air conditioning works fine!

Control unit unmodified?

Hmm, is it a used car (maybe the previous owner?)
"But I once had an inexplicable error, so I replaced the LMM (on the advice of a friend), and it went away. However, the error back then had absolutely nothing to do with the LMM. Still, it's been quiet ever since."