Question about our food freezer - freezing up?

Perhaps you have set the dial inside the freezer on MAX, try turning it down to just over half,as that will still keep food frozen. Also seal may be cracked/broken,letting in moisture which then adds to the frosting problem,a good clean with a mild detergent on the seal,and where it makes contact with the metal will also help. Check detergent is ok for rubber/plastic!

More than likely your defrost heaters are defective. go to www.searspartsdirect.com with model number and look them up. Call round to local appliance parts store or order them from sears. Defrost the freezer like you have been doing, pull out shelves in freezer undo the backwall and the heaters are located there. unplug them (they have a quick disconnect) remove the old plug in the new and put everything back the way you took it apart and you should be good.

Replace the defrost timer, and/or the defrost solenoid. (the solenoid is good if it has continuity) -Look online or in the lower rear of the unit close to the compressor for the wiring and component diagrams. There's a good chance of finding the part at most any online appliance repair parts warehouse/dealer; make sure to have the EXACT make/model/serial #'s on hand and ready for the order.

freezer is not going into defrost mode, you have 1.a bad timer 2. a bad bi-metal thermostat or 3. an open heater element, you need a serviceman to fix

You could have a bad door seal(if 5 or more years old) or it could be the defrost timer (if frost free)