Ice forms in freezer - Sub-Zero 19.3 cu. ft. / 547 liter Upright Freezer 601F

Use a steamer to blast the drain clear... sometimes you need to install what is called a heat probe that feeds into the drain tube to keep it from freezing over... Help Me Find My Model Number RepairClinic com

is the top of the freezer full where it can breathe remove something to help it breathe

sounds like a defrost problem there should be a defrost control and some form of a heater onthe inside of your freezer you should call a technician for proper diagnosis on which part you will need

dependant on appliance you may have a small drain hose at the base of the appliance that drains the defrosted water away at regular intervals. Sometimes this blocks and the water that should drain away just starts to freeze over.

Very possible the door seal is not properly sealed. Warm inflowing air onto a cold coil will cause ice build up at the lid.

1. You need to unthaw the freezer, and it should start working.

Low temperatures are absolutely required for proper operation of ice makers components. Dirty cooling coils or possible low refrigerant.

The cause if no defrost cycle , remove the panel where the ice is and derost with unit unplugged , use a hairdryer or similar to defrost ice , make sure its all defrosted , check the heater under that coil to make sure its still intact.
Also check the defrost timer , there may be a wiring diagram on the back showing where this is located.
Phil

Not sealing. warm air hitting cold air causing frost. also, door frame heater may not be working. most frames are "warm" to the touch. normally called an "anti sweat" heater.

might have the temperature too high .. buy a freezer thermometer and place in freezer