Originally Posted by albannach
Yes, the coolant line containing the compressed refrigerant run all through the walls of the fridge, and since it's an old fridge, it probably still has some type of toxic or environmentally damaging coolant in there. It is usually safe to drill through the door of the fridge though.
Not always. It depends on the design of the fridge. I have an older one which has the evaporator coils in the top, back and bottom of the freezer compartment only. The condenser coils are on the back and mounted externally. I just drilled through the side for a temp probe yesterday with no problem. I would suggest locating the evaporator and condenser coils. Don't drill until you are certain of their locations. If you do not see visible external condenser coils, you can feel the sides, top and back while the unit is running. The concealed lines will be very warm to the touch and so will the outside wall of the fridge if it contains condenser lines. Much the same inside the fridge, but the evaporator lines will be cold. There are also lines running from the compressor to the evaporator and from the evaporator to the condenser then back to the compressor. These need to be located also and that can be a bit tricky sometimes. If you are not sure where everything is, drill a very small hole and probe around in there. Enlarge the hole and when you are fairly sure nothing is in the way, go for it.