Samsung SR-L3616B cool n cool

Hello fridge gurus. Hopefully this is an easy question to answer, it has me stumped but I’ve not looked into a fridge before (other than for beer obviously!)

I have what seems to be a common problem for the SR-L3616 ‘cool n cool’fridge freezer. It cools down to -25c (checked with thermometer), cuts out and restarts when Mains switch is reset. I have opened it up and checked the defrost heater cable has continuity(as suggested somewhere online), the two yellow thermostats , (one in the air flow, one on the evap) have full range. There is a small device attached to evap beside thermostats which I don’t recognise which has zero resistance both when at warm air temp and at max cold. Is it some kind of switch? Is it the problem? Is it something else.

Please help, all the dog food is defrosting and my dog will burst of it had to eat it all at once.