I haven't seen anyone mention something like this before, so i'll post this since it might save a few of you from buying the Johnson controller when you need not:
I just bought a $25 mini fridge from a student at the local university where I work (students have to move out of the dorms for summer, so there's plenty of good deals on craigslist right now). Its Sanyo model A2480m and only 1 year old. On its lowest setting (1) it only gets up to 40F. I wasn't happy at the thought of spending double that on an external Johnson controller; just didn't seem right in a volumetric sense of value. I did notice that the thermostat in the upper right of the fridge was rather large looking. Hmmm, decided to unscrew the cover (after unplugging the power cord) and found inside it the Chuzuo Phoenix Automatic Controller TD-004-P2102 with a few wires sticking out, plus in the middle was a thermocouple (a metal tube that looks larger than wires, in the photos below you can see it is the one with the white plastic cover). Ends up that there's a calibration screw on the top of the controller, right in the middle near where the thermocouple comes in. I tried to google the controller in hopes of finding a spec sheet, but no luck. I decided to loosen the screw and see what happens. An hour later I see the fridge now goes to 42F. Over the next few days I fine tuned it and now it stays in the 52-55 range, just perfect! There's another screw on the bottom of the unit but i'm not sure what that does.
So, a $25 mini fridge, no external controller needed. Don't know if every mini fridge is this easy, but its worth checking. Just remember to unplug the power cord before you start opening it up, otherwise those wires on the thermostat controller have 110V! Below are some photos. The calibration screw is visible in the second photo, to the left of the black wire.