Well, I have read that when I bend down my freezer in my new small fridge as part of my kegerator conversion that the fridge will freeze everything up as all the cooling for the fridge is via the freezer bottom plate (that will get bent down).
This necessitated an external thermostat so instead of buying a digital Johnson Controls A419 at $75 or $80 I went with a home made thermostat based on a $20 digital controller, a STC-1000. This is sold off of ebay from China and a common homebrew DIY item.
The build was not too difficult, it required a ‘project box’ (from Radio Shack) for $7, and a 8ft power cord ($8). I made mine slightly different than most people who do this, I only wanted cooling, so I did not install a plug in socket, and instead just used the female end of the extension cord that I used for the power plug-in. Worked well!
Here is a video with a similar setup, he uses a outlet and heating on his though – my setup was a bit easier.