Freon, a type of refrigerant, helps to keep a refrigerator at the designated temperature. When the Freon gets low, the fridge may fail to keep food cool enough to ensure food safety. Low Freon could indicate a leak in the system, as Freon doesn't dissipate but rather leaks out. A small leak is often hard to detect. If the leak is not repaired, the refrigerator can't be recharged, as leaking Freon is harmful to the environment. Instead, the fridge will need to be discarded properly.
Look at the food stored in the refrigerator, or freezer, and determine if the products are cold enough. Particularly, check the ice cream to see if it is soft, or if the ice cubes are frozen. If you notice that the fridge is not keeping food products cool or as cold as before, it may need a Freon charge.
Pull off the kick plate at the bottom of the fridge or on the back of the unit. Look to see if frost is covering the coils. If frost is not covering the coils, or is only covering some of the coils, the fridge may need more Freon.
Set the cold control knob to "Low." Look at the top of a "frost-free" refrigerator. If frost is visible inside the fridge at the top of the unit, there is Freon, but the thermostat is most likely faulty.
Turn the cold control to the "Off" position. Place your ear against the side of the refrigerator and listen for a hissing or gurgling noise. This noise is made by the Freon equalising through the capillary tube. If you can't hear this sound, then the unit is low on Freon.
Freon is a highly toxic substance. Never attempt to recharge your refrigerator on your own.