Samsung sr-s2028cvw testing sensors?

I have a remarkably similar fault as several people on this site! the fridge/freezer switches on and runs and cools to -20 freezer 3 fridge at some point the temp indicator on the freezer starts to flash and the cooling stops but the display still reads -20 and 3 degrees. the fridge is able to cool so compressor and condensor are effectively ruled outwhich lead me to conclude the offending fridge freezer seems to have a sensor fault, I carried out the onboard diagnosis routine (top two buttons simultaneously for 10 secs) but no segments of the temp leds illuminate, I have been researching these posts quite deeply and have come across conflicting conclusions, Firstly I have been told the thermal fuse, and cooler fan is faulty! This seems implausible as on “reboot” the fan at the rear of the unit spins (I assume this is the cooler fan) so I am reluctant to condemn this. There are 2 thermal fuses in the system, fuse F and fuse R both of these have continuity as this can be checked at connector 70(White plug) at main pcb on the brown wire via defrost heater, and defrost heater R white wire of the same plug, upon checking both are ok (unless they are resetting before I am able to test for o/c) my original thought was perhaps one of the sensors was faulty,exterior or ice switch? however my knowledge of this sensor type is minimal eg is it digital or analogue signal and what reading am I expecting if I test it? hence this post, any help would be appreciated, I am fairly confident and competant at indepth fault diagnosis, any helping samsung engineers out there willing to share knowledge? thanks in advance