What fridge temperature in hot weather?

Does anybody know what is a reasonable lowest temperature that a new caravan fridge can reach in hot weather? In S France this year with about 32 deg outside we could only get our newish Dometic down to about 8 to 10 deg C. This was on trying gas, electricity and different control knob settings from min. to max. This temperature is in the red zone on our fridge thermometer and I would expect to be able to get down to 4 deg. I think the freezer compartment stayed quite cold though.