mbadem,
Ideally, the temperature inside your fridge should vary only minimally with the outisde temperature so it sound like either the door gaskets are leaky, the door
latches are not closing the doors tight enough for a seal, or your box may not have enough
insulation (or any combination of the above.)
To answer your question you should be aiming for an inside temperature of about 38 degrees F (3-4 if you're of the Centigrade persuasion) so a setting of 2 o3 three should prevent your soda cans from exploding while keeping your other
food from spoiling>
I would also check the door gaskets for
leaks and your door
latches to see how tightly the keep the doors shut. My fridge has about 6 inches of
insulation and door latches like the latches found on
commercial freezers. (There should be a
photo of it among my images) Just recently, with the tempertaures in the 20s the box was maintaining its 38 degree temperature inside.