Ice build-up in the freezer of a Kenmore 19 (Top Freezer) refrigerator, and only 60 degrees in the fridge.

Local "repairman" replaced the burned-out Freezer fan last week, but frost/ice continues to build on the Freezer abck wall and in the vertical cold air conduit leading down to the fridge compartment. I'm scraping off the ice near the fan every day to try and stop the new fan burning out as well. This 20-yr old model (2538359202 Top Freezer) has the optional ice-maker NOT installed; it has no obvious DEFROST manual switch; the water pan at back on top of the compressor motor is bone dry; No removable access panels in Fridge section, only in Freezer; Evaporator coils on back appear quite dust-free; Power Miser set to ON; Fridge set to COLDEST and the freezer set to WARMEST. It's in a vacation home in Florida, and is turned off 9 months of the year, but badly needed now. Seems in too good a condition to just toss it. I'm fairly handy (electrics & mechanicals, but no multimeter or heavy workshop) Please help!