Why does my freezer get a little warmer every 14 hours?
It is defrosting.

Frost free refrigeration equipment goes through a defrost cycle every few hours. This normally involves turning off the cooling compressor and activating a heat tape that is attached to the evaporator coil for about 20 minutes. This melts any frost and ice that has accumulated on the evaporator coil and keeps it from accumulating.

It is completely normal to the operation of modern frost free equipment.