A freezer is only as good as its thermostat is accurate. A broken or malfunctioning thermostat can render a freezer useless and can destroy its entire contents. Freezer thermostats can be replaced at home with a few tools and the right technique.
Turn off the freezer.
Locate the thermostat on the outer door or inside the freezer, depending on the model of freezer.
Remove any screws or panels holding the thermostat in place with a screwdriver. Pull the thermostat from its housing.
Remove the wires from the thermostat. Use needle-nose pliers if the wires are pressed into place or a screwdriver if they are screwed into place. Freezer thermostats generally have five types of wires: brown (power), blue (neutral), green (ground), black (compressor), white (lighting).
Connect the new thermostat. Connect all the wires to the new thermostat in the same location as the old thermostat. Most thermostats have a wiring diagram on their surface which labels the different terminals.
Replace the thermostat in its housing. Replace any panels or screws and screw the thermostat into place with a screwdriver.
Turn the freezer on.
Plan for your food storage. Frozen items in the freezer can melt during the thermostat installation process, so plan for the amount of time the installation will take and alternate places to store any frozen items.
All power to the freezer must be shut off before performing any maintenance.