Interior is not getting warm Omega A

Hello, I have to describe my problem here again, but now with more basic data: Well, my interior doesn’t get warm. The engine temperature is about 80°C for this season. The hoses to and from the heat exchanger are both hot. I looked at the heating adjustment, all the trains are at the places where they belong. As I could see from the outside, all flap adjustments move, as I said, as I could see from the outside. If I put the heater on warm, d The lower adjustment lever on the middle, the upper lever on the disc, comes up only a lukewarm vent. If I place the heater on cold, I have up full blower power. If I place the heater on warm, and the adjustment lever down, comes down right (passenger side) warm air, down left (driver side) only a lukewarm vent. The blower works properly. The only thing I can still think of that within the ventilation mechanism a little broken, or snapped out o The biggest problem will be: How do I get to these ventilation flaps etc. without expanding the entire dashboard? Can someone help me? Thank you very much. Greeting Omega40