I had my fridge outside for a while during a kitchen remodel, and below 40F, it wouldn't work and the freezer goods would start to soften. Luckily it would kick in again during the day and refreeze everything. The fridge still works now that it's inside again though. So your most likely problem will be your beer may get up to 45ish degrees if ambient temps are just right for long enough. Or if it gets below freezing in your garage, your beer could freeze.