While many of us have enjoyed the convenience of the spare refrigerator in the garage over the years, there is some truth to warnings that such a device will not run properly. Refrigerators are designed to operate within a typical indoor temperature range of about 60 to 100 degrees. Garage temps can run between -0 and 100+ degrees, and because the freezer is set to come on only when the refrigerator is working, it may actually warm your frozen food and cause it to thaw and spoil.
Some manufacturers make refrigerator/freezers specifically designed for an unheated garage. If you don't have one of those, my recommendation is to keep a close eye on your refrigerator's temperature--especially in the winter--to make sure it's doing the job. One other tip: many garage outlets are protected by GFCI's (ground fault circuit interrupters) and are not designed to support a refrigerator. As a result of the compressor going on and off, large voltage draws across the circuit can fake the GFCI into thinking a short exists and it will turn off the circuit and your refrigerator! If you are going to add a refrigerator to your garage, have an electrician install a dedicated, non-GFCI-protected single outlet and use it only for the purpose of plugging in the refrigerator.