Not sure if this has allready been posted and I assume it has due to the depth of the information on this site but here it is just in case. While I am sure there are lots of really intersting ways to find the coolant lines in any fridge/freezer you plan to make a kegerator this is the way I do it and well....it works.
1. Find your local fire station, take them some cookies or a box of ice cream. Then ask them if they have "thermal imaging cameras". They probably do and they are awesome little portable units that read heat differentials in material. Now being a fireman myself I can say they should all be fairly receptive to pulling out the camera and taking a quick look at the walls of any cooling unit in order to see where the lines are run. I would suggest plugging the unit in and then when its good and cold making a quick run for the fire station before it warms up to much. The whole process with the camera should take about 2 minutes, that involved going out to the fire engine to get it.
While most guys and gals in the fire service would be happy to take a few minutes out of the day to make a citizen happy it can also be said that in a certain way..........everyone works for homebrew.