Starting this one off with no guarantees! I did this with a $20 digital temp controler off amazon before I knew ST existed and I haven’t used my ST hub to manage this task.
But if I did it again I would do this:
Using a temp sensor:
SmartThings SmartSense Temp/Humidity https://www.amazon.com/dp/B00MOJBR0M/ref=cm_sw_r_awd_AG.Vvb529NTGB
At this point I would pair the sensor with the ST hub. Next with the fridge off but plugged into the wall ensure a consistent connection to the hub with the sensor inside the fridge(door closed). Most fridge exteriors are a ferrous material and this can interfere with RF signals. Additionally grounding the fridge can effect the amount of the interference also. That’s why I suggested having the fridge plugged in during your testing.
If the sensor passes the signal test my next goal would be to prevent the sensor from being damaged by moisture. You could possibly skip this and try your luck at the sensor being ok. But again, this is what I would do…
NOTE: this method will void any warranty the sensor may have and could render the sensor inoperable.
Purchase some Rust-Oleum® NeverWet® this is a two part kit.
Open the sensor exposing the electrical components. Following the NeverWet instructions coat the sensor and remember you need to cover the front and back of the circuit board. I’ve used this method to make several electronic components water resistant with 100% success. I have a Z-wave vibration sensor literally floating in my pool. It detects water disturbances(waves) to signal an alarm if someone falls into my pool.
Using a plug like an: Aeon Labs DSC06106-ZWUS - Z-Wave Smart Energy Switch https://www.amazon.com/dp/B007UZH7B8/ref=cm_sw_r_awd_S7.VvbV1C0NF0
Set up (Keep Me Cozy II) to use the fridge thermostat and switch on and off the plug at your desired temps.
Threw this together quickly with Siri while mowing my lawn so if it’s a little ruff sorry.