freezer defrost failure - ice up - temperature rise

After replacing the defrost timer (easy: pop off the grill; unscsrew the bracket; pull out the old one and plug in the new one) [didn't fix problem] and replacing the defrost heater element (harder: use nut driver to remove ice maker and rear interior panel in freezer section; use pliers to remove clips holding the heater element to evap coil CAREFULLY - puncture evap coil and unit is junk!!! - replace with new heater element)[didn't fix problem] I replaced the defrost thermostat:
moderate difficutly. Use nut driver (5/16") to remove ice maker (loosen screws and slde IM up and off) and rear interior panel (don't need to pop the ice maker electrical connector off the rear panel) and unclip the thermostat from the evap coil. Replace with good thermostat and enjoy your "self defrost" freezer/fridge for another fefw years.