Our fridge freezer recently began to have temperature problems, both the fridge compartment and the freezer compartment struggle to keep cold. the compressor is constantly running and the fan runs sporadically. We have taken off the case in the freezer and defrosted the Radiator. the temperature seemed to be going down at a fairly decent speed but it then stopped at around -7 and went up to +6 then down to -19 then again up to +8. Could this be a sensor issue? what resistances should i be reading over the sensors?

any help would be appreciated as we are out of ideas.