I converted an old fridge that did not have very good temperature control....into my cheese cave.......I invested in a thermostat control box from my homebrew shop....it is the cooling one.....it will cool between 0 and I think 40 degrees celcius......(there is also a heating one)
This control box is plugged into the wall and the fridge is plugged into the control box.....the new 'thermostat' bypasses the fridges thermostat.......it is all tested and approved with Australian Standards....so thats why I didn't bother with trying to make one.....much safer this way..
Above you can see the coil coming through the fridge wall, this is the only modification I made to the fridge, no wiring, no electrician needed....I have the probe in a glass of water to eliminate temperature variations when opening the cave door.
You will also need a hygrometer, that's just a fancy name for something to measure the temperature and the humidity....I got mine for $19 from a hydroponic supplier on ebay .
You will notice that I have two devices measuring temperature....you don't need two, I just started with the round one and upgraded to the digital one later.