I'm sorry for those big images, tried to change them to attachments, but it cant delete post.
Yesterday I changed the Cabin Temperature Sensor and found what is wrong with the old one. Looks like it has a small cooler built in which was stuck and it gets hot after a while, and thats the reason for the high temp. The cooler on the new one spins and temp looks good. Too bad that problem doesnt trigger an error in HVAC. I have attached some photos with the sensor, its location and the parts you have to take off to change it. If someone has questions or needs more photos, I would be more than happy to help. Cheers!
My pleasure, glad to be useful. The Lancia Thema is the same with 300C, just different badges. All cars have this type of sensor, only the location differs from type to type. For example, my 05 Fiat Croma which has climatronic also, has this cabin temperature sensor near on the dash unit. What year is your 300C? I will search for info.
My model year is 2006, so an early design. I think the cabin temperature sensor is on the front dash and I don't recall seeing any reference to "climatronic" in the Owner's Manual. The side panels of the facia do not have any openings, as shown in your photos.