The Winter Problem. You'd think it should work better when outside temps gets cold, but no. (This happens with commercial walk-in compressors that aren't winterized, too).
It's a physics problem dependent on the design of the a/c unit. As temperatures drop the unit can't circulate coolant fluid properly and a safety is tripped. To reset some units UNPLUG-and-REPLUG your A/C unit when it warms up. Frigidaire suffers horribly from this problem even below about 40F outside! Other AC's will work in temperatures down to freezing. If you have an air conditioner with automatic re-start it will come back on by itself as soon as the temperature warms up.
If you have a Frigidaire (or similar brand) and need to run in the winter try keeping the back of the a/c unit in a warmer area. Inside a garage or barn for instance. A restaurant in New Hampshire has 2 holes in their walk-in cooler - In summer it's mounted outside the building and in the winter it's mounted with the back inside the building to add “free-heat!”