Hi Eddy
I have an 80 litre Waeco fridge freezer with three compartments. I always run it at -18, as that allows the freezer section to operate, and the other two sections stay cool from that. That is how the supplier that I bought it from told me to run it, and never had a termperature problem. I have had to replace a couple of clips, but nothing else in four years.
Regards
Tjupurula