Hello, Alarm is triggered when ever the temperature inside is above its working temperature. Either freezer or fridge is above it working temps, the alarm will be triggered.
If you have a place to put the food in the unit so it would not spoil, I am suggesting that you defrost the unit completely for 24 hours, with both doors left open, to make sure all the ice inside the evaporator would melt and the coil will be free of ice before starting it up again the next day.
After you plug it in, the alarm will still be triggered but should stop after a few hours if the temperature inside the unit would reached it set temperature.
Let me know the development please.