Beko CF5015APW fridge compartment too cold and won’t defrost

I have a Beko CF5015APW fridge/freezer and the fridge runs too cold at 2 degrees with the temperature control knob is at 1. The freezer runs at -20 degrees. The cooling panel at the back of the fridge doesn’t auto-defrost.

I replaced the PCB control electronics at the rear of the cabinet, which made no difference.

I measured the resistance range of the temperature control potentiometer and it is working, however, I can’t remember the readings.

I thought the problem was a faulty fridge sensor, located under the foam insulation just below the PCB, however, its resistance is 26K ohms at around 0 degrees C, which sounds about right.

Given these symptoms, (auto-defrost not working and fridge running too cold) what do you thing the problem is please? Thanks.