Kenwood KSBSW17 American Fridge Freezer. Fridge not cold enough

Hi All. Need some tech advice as I am am out of ideas. Bought an “appeared to be working” second hand KSBSW17 the other day. But having installed it at home I find the freezer side all working O/K at -18 deg c and will go to -20 deg if required. Fan going O/K.. However the fridge side will only go to 8 deg C even if I program it lower from the front panel. To date I have changed the front panel. Changed the flap assemble that comes from the freezer side. Changed the Thermistor that sits inside the fridge area. None of which has changed this fault. The only thing left iin my mind s check the condenser pipes underneath it for dirt (cant believe this could be the cause) and that means lifting it somehow? Or changing the main PCB. Anyone got more idea.