We have a Whirlpool side by side in our garage that all of a sudden has stopped freezing on the freezer side. We are not sure if the refrigerator side is working properly as our temps have been so cold outside that it could be aiding in our items being cool.

The question is has the unit run correctly in the past when the ambient temperatures have been that low?
If it is too cold outside the compressor will never come on and therefore no freezer. On top of this the defrost cycle still runs but the heat collects in the unit as the compressor never turns on after the defrost so everything in the freezer melts.

If the compressor is running remove the evaporator coil cover and check them.
If they are heavily iced/frosted up you probably have a defrost problem.

If they are just frosted up in one area you may have a low freon problem.