I had a Hoover fridge/freezer which was condemned due to insulations failure, so I used it to brew beer in, I wanted 20 degs C so used an external thermostat to control.
While setting it up I found the freezer only seemed to work, and it seems it was designed to give freezer priority and only once the freezer was cold enough would it start cooling the fridge.
OK for what I wanted started brew in freezer and conditioned it in fridge, but it seems if for any reason the freezer can't get cold enough, then the fridge will not cool.
After having the problem with that fridge/freezers insulation I started to monitor the other units to see if there was a problem, so looked on internet at yearly power use, divided by 365 so daily use, and measured the power used in a day, all used over the figure the manufacturer said, but not by much, except my mothers, looking at running power and daily power it was clear it was not turning off.
I went around all local shops looking for a freezer thermometer, but no one seemed to stock them, so made up some brine, freezing point of brine (saturated salt in water) is -18 degrees C so it should just freeze, but will take a day or so as freezer should be at -18 C. It froze solid, then the thermostats I had ordered for brewing arrived so used them to monitor and it confirmed -27 C the freezers thermostat was faulty, this would explain why mothers ready meals needed extra cooking time.
So new thermostat ordered and fitted, however the spindle was not long enough so can't adjust once fitted, but motor does not switch off.
Be it thermostat failure or insulation failure or loss of gas the result is the same, motor never turns off, the thermostat was cheap around £5 but tried to get one local and failed, all I could find were refrigeration repair men, who had a call out charge of £60+ and then cost of repair first hour covered by call out, the freezer cost £100 new so simply not worth it.
But the energy meter was cheap enough, I had all sorts of ideas of how I could use the meter after, however in real terms only used to monitor fridge/freezer.