Freezer not freezing but cool

Kenmore model 106.62159111. The freezer is cool but not freezing. Temp in freezer is about 20 degrees. Took the back panel off in the freezer and there is some ice build up but it wasn't alot, on the right top corner of the evaporator. Took a blow dryer and removed the ice and plugged it back in. Could it be the defrost heater and/or the thermostat? I'm just wondering if it's worth getting a 9+yo frig fixed or just buy a new one. Thanks