fridge freezer not freezing enough?

I have just bought a second hand Hotpoint under worktop fridge with a small freezer compartment for our caravan, i have put it outside in the garage to try it, i have set the temperature control to full,allthough it is coldish to the touch it dosn`t seem to get frosty in the freezer compartment or cold enough, what might be wrong with it please. thanks in advance for any answers.