In order to test that a refrigerator is cold enough, the experts recommended placing a liquid, such as water, in the main compartment for at least 24 hours.
Then remove it and check with a thermometer. They advised doing this test with a liquid as this is more likely to cool at the same temperature throughout rather than a solid substance that will cool at different rates due to its density.
From KJ Refrigeration, they explained people should avoid having a “full fridge” as this will consume more energy.
“The air circulation in a fridge helps keep food fresh, so you should keep your fridge around 25 percent full.