We tried to do this when we first finished the pole barn. It worked great in the summer time, but not in the winter. This was in '05 & '06. Once it started getting cold, it wouldn't run. Stuff in the fridge part was cool, but not cold. Stuff in the freezer thawed. If I remember correctly, it has something to do with in old fridges they put the thermostat in the freezer and in the new ones it is in the fridge part. Needless to say, it didn't work. Once we finished the new house we took the 2nd fridge out of the barn and put it in the utility room of the house. Not as convenient out in the barn when I want some pop or water out in the barn in the summer time. We have an old deep freeze unit out in the barn. It works fine year round - though in the summer it costs quite a bit to run it because of the temp extreme. We have unplugged it now and don't use it. I will probably plug it back in and let it run for a while to keep it from seizing up on me.
I'm thinking about buying a small dorm fridge to keep in the barn for pop/water in the summer time.