I've read most posts dealing with the coils freezing up in the freezer side of GE models similar to mine ,TFX20JRSMWW. My unit was purchased around 1996-97. I have replaced the defrost timer and the heater elements/defrost thermostat assembly. After 3 to 4 days, the lower portion of the coils still freeze up and do not defrost. This isn't heavy frost, but ice block. I have taken the back panel out and observed the heating elements when it goes into the defrost cycle. Top element burns bright orange, while the lower element barely gets orange. I ohm tested these parts before installing them. Both elements tested OK. Are these elements supposed to heat at different levels? Any help is appreciated.