For the moment I just disconnected the heating element and wired in a t-stat from a mini fridge. The heatin element could very well have been broken as long as I owned the fridge (it was given to me as a quite old 2nd hand fridge).

I guess I will keep my eye out for similar normal sized fridges that are trashed. Maybe I can harvest a heating element and combined t-stat like mine to recover the auto-defrosting function.