When you adjust your refrigerator's thermostat, a device called a thermocouple does all the heavy lifting to maintain the desired temperature. This built-in thermometer signals the fridge's compressor to shut down once the interior compartment reaches the temperature setting you've chosen; it also tells the compressor when to come back on when temperatures rise.
The thermocouple is key to how your refrigerator operates, but there's another crucial element that regulates your ice box's temperature: you. Knowing the ins and outs of temperature control and understanding ideal temps helps keep your food safe, your fridge ticking and your energy bill consistent.
Many modern refrigerators come preset at a factory-recommended temperature -- when you need to tweak the temp, the process for doing so depends entirely on your specific appliance. As such, the manufacturer's user manual is the perfect place to start. Like adjusting the thermostat, the time it takes for your appliance to reach the desired temperature depends on the make and model.
Some refrigerators feature a digital control panel on the front of the door, allowing you to adjust the temperature with the press of an "up" or "down" button. Other appliances use a simple dial for temperature control, while -- more rarely -- some fridges feature temperature switches that allow you to cycle through factory-determined "low," "medium" and "high settings," or a range of temperatures ranked in coolness from 1 to 5, for instance.
The U.S. Food and Drug Administration recommends maintaining a refrigerator temperature of 40 degrees Fahrenheit or less. A range between 32 and 40 degrees works well, with an ideal sweet spot of about 35 degrees Fahrenheit. Items may begin to freeze under 32 degrees or attract bacteria at temps over 40.
Expect some natural variance in temps, though. While areas near the bottom and back of the fridge stay the coldest, the door shelves can reach temperatures in the high 50s. Be mindful of how you place your food, keeping condiments, butter and the like in the door and particularly temperature-sensitive items -- such as milk and meats -- in chillier areas.
You can't regulate your fridge's temperature without knowing exactly what it is. Some modern appliances feature digital readouts, but if your refrigerator is thermometer-less, you can pick up an appliance thermometer for just a few bucks at your local grocer, appliance dealer or hardware store. Place it right in the middle of the interior compartment for accurate readings.
Alternatively, you can use a bulb-type candy thermometer to get a reading. Stick the thermometer in a food or liquid that has been in the refrigerator for at least a full day and let the device rest for three minutes to get an accurate temperature.