This is a slightly stale thread but as I've been trying to figure out how I want to proceed with my chest freezer/refrigerator/fermentation chamber/keg serving cooler (ha) I've been doing some research.
Often times, you can tell how a refrigerator is built by looking at repair site drawings. Most of the freezer/refrigerators I've been looking at have drawings on sites such as Searspartsdirect.com or other repair sites. The drawings show the evaporator coils for most of these models being behind the back wall of the freezer section. True, there may be wires in the floor of the freezer but you can obtain clues on the repair site as well. Many of the inexpensive freezer/refrigerators use a bimetal thermostat, which runs straight back along the ceiling of the refrigerator section. There may be other wires but if you're determined to cut, and you can't tell exactly where those wires run, just punch through with a screwdriver and slowly widen out the hole to expose the insulator layers.
Make sure you identify drawings for your exact model of appliance. Otherwise, you're taking your chances.
These freezer/refrigerators really aren't that complicated. As has been mentioned, they're usually cooled by the freezer alone. Basically, when the refrigerator temperature sensor rises and hits it's trip point, it opens the damper and runs a fan to circulate cold air from the freezer. When it goes below it's set temperature, the fan turns off and the damper closes. I'm not an appliance guy so I can't say it there's any electrical connection between the refrigerator functions and the freezer. I suspect not.
My current project is to determine if I can split the refrigerator section of a freezer/refrigerator in two, add a damper to the added section, bypass the bimetal thermostat and use one side for a conical fermentor, the other for keg chilling. I'm playing with the idea of putting a wall into the freezer section to make it smaller. As others have mentioned, the freezer doesn't need to be so large. I may cut a hole in the ceiling of the keg chiller section, up to the front of the freezer (with the installed wall behind it) and installing taps into the freezer door. We'll see. I'm still searching this site to see what others have done.
As always, I'd appreciate any comments that could both point me in the right direction as well as steer me clear of disaster. My brain tends to skew towards disaster.