Why does digital display state is -21 when infact its warm inside both ?

Hi, i actually work for a repair company and we are struggling to understand whats up with my fridge its an american LG gs5163 and is not working in both fridge or freezer the compressor is running not over heating ,so must be gas in the system, but the digital display shows - 20 or what ever you select it to which isnt the correct temp inside clearly as its warm, was delivered lying down could this be a factor???? but im thinking its got to be a sensor fault as why cant it read that the freezer isnt cold??? also no error codes are coming up so cant even narrow it down so its very akward fault, hope someone can help.