Ge frig tfx20jrbkwh is freezing up . defrost htr is burnt . does this unit have a def timer ? where and how do i test it ?? also the wiring going to the htr has a round thing clamped to coil should this be checked or replaced ??

Good day,
The timer is located behind the plastic light guard in the fresh food compartment. Remove thermostat knob, then unclip the guard.
The timer is behind the guard and is behind the metal panel.
It has a small hole where you can insert a small screw driver to advance it.
It will only turn clockwise. With the machine running, turn it clockwise until the machine shuts off. With the machine still turned on wait a minimum of 35 minutes. If the machine comes back on on it's own, then the timer is O.K.
If not, then the timer must be replaced. Remove the screws holding the the panel on. Remove the screws holding the timer, and remove the electrical plug.
P.S. This timer rarely fails.
To replace the heater, I strongly recommend you use the new kit that has 2 not one heater. The round thing your describing is the defrost thermostat. Always replace it if installing new heaters.

The parts are available at any appliance parts house that carries GE parts. Take your complete model number and request the parts I described. This is a common problem, and any good counterman will know what you need.

Patience is your friend here. Those quartz glass radiant heaters are easily broken if handled roughly.
Thanks for using FixYa.