If the evaporator coils behind the back panel of the freezer are icing up it's because of auto defrost failure that will stop the circulation of cold air.
check defrost timer, defrost heater, defrost thermostat
In most of the new units they now have the evaporative defrost control. It senses when to defrost based on how many times and for how long the door is opened. It's more energy efficient but there does seem to be lots of problems with the board.
Post your model number for information on whether your have timer or evaporative control. | 
Condenser keeps freezing 
