Freezer AEG noFrost, compresor work non-stop

Aeg 2794GA Typ 73 FBA03..; E-nr.625551128
The compresor works over riching setup temperature:-15’C (set-up) after half hour self electronic read -18’C (tester reading temp=-19’C) and he dont stop. he work so even day &night….
So I suppose the sensors are Ok but before to dig in electronic I would know if is other thing. Perhaps one direction will be useful.

Thanks 8)