Chris the defrost timer is located inside the control panel in the fresh food section.
Now that you have defrosted the unit,run it for 24 hours,then use a flat scredriver to turn the defrost timer clockwise until the unit cuts off.
You can then put a amp meter on an incoming power wire to test for a load on the heater.
It should read about 3.5 amps.
If no amp draw is present replace the defrost thermostat in the freezer.
The heater(calrod) is most likely good.
If you do read 3.5 amps or better,replace the defrost timer.