Depends on the fridge
Part number: AP3722172

OK looks like your unit is an older type with a thermostat so you may be able to use this kit. It is for a Frigidaire so you will probably have to mount it a little different than what the directions say.

Kit is for a top mount fridge.
Unit must be the type that uses an old style thermostat.
Newer electronically controlled units are a no go.

The reason food is thawing is that the defrost heater comes on, adds heat to the freezer but the compressor never comes on to get rid of this heat because of the ambient temperature itself is keeping the unit cold.
Basically this adds heat to the thermostat so the compressor will start.

This should allow you to run the unit down to around freezing.

If your exterior temperature is dropping much lower than freezing then I would not recommend it.
The compressor has oil in it which thickens as the temperature drops so very low temperatures put an extra stain on the compressor motor when it tries to start.

Here is some more info
Appliance Talk: Refrigerator in the Garage