Our GE s/s TFX20JR was not chilling in the food compartment. We unthawed the coils and now it is running and cutting off periodically. Do we need to change the thermostat or the heaters? I assume this will happen again.

This is a very common problem with side by side fridges.
1. Defrost heater faulty
2. Defrost limit switch faulty
3. Defrost timer faulty

If you have a multitester you can test each component and see which one needs replaced. If you have a motherboard arrangement in the unit that entire board may have to be repaired.

I had a side by side Frididaire that had the defrost switch go bad THREE times in less than 2 years. That was back in the early 1990's.