GE Model number TFX25PPBE BB where is the defrost timer located and what does it look like?

hello , hope this helps
your model shows that your model has a main board . the defrost timer is now a main board and everything runs through that board. behind the ref . square cut out by the btm with 6-8 screws that hold the cover in place.

There is not a defrost timer on a model PSC23NGN. If your model is the=> PSC23NGN and the refrigerator is not defrosting the problem is most likely the Defrost Heater and Defrost Thermostat that need replaced. The heater is item location 230 and the defrost thermostat is item location 240 in this photo=> HERE
The part numbers for the Defrost Heater are WR51X10055 Defrost Heater Assembly The part number for the Defrost Thermostat WR50X10028 Defrost Thermostat
I am here if you have questions, Thanks John Tripp
Appliance 911
Contact me here.

most ge timers are located on the main control board on the back of frg.it is covered by a 4x6in plate

Where is the defrost timer in my General Electric freezer model number PSS26NSTB SS

Not every refrigerator has a defrost timer. Those that do will most times have it behind the controls inside fresh food campartment or just behind kickplate at front and base of refrigerator. What is your model number?
Here are some examples=> GE APPLIANCE MODEL NUMBER LOCATOR'S

Refrigerators

• Side-By-Side
• Top Freezer
• Bottom Freezer
• Wine and Beverage Center
  Thanks Sea Breeze

The defrost timer is located in the freshfood compartment at the top of the back wall behind the light lense.

You frig is not going through the defrost cycle. Locate the defrost timer and advance it to the defrost cycle.(one click). Empty the freezer and remove the rear panel. See if the defrost heater is starting to get hot. Located at the bottom of the evaporator. If getting hot, replace the timer. If not getting hot, unplug the frig and check the resistance across the defrost timer(should be a closed curcit when cold) and across the heater. If "0" resistance, replace heater.
When replacing the heater alwarys replace the defrost thermostat at the same time. Will save you work in the near future.

If your model is the TFX27PFSM BB I only see a simple defrost timer. But not to say that you possibly have a bad thermistor that came on some models. Part number 305273 This is an alert so I would keep a close eye on freezer and refrigerator temperatures. The defrost thermostat may be defective and the light is warning you of a problem coming. Let me now if I can help you more, Thanks Sea Breeze

To solve this I need the model number of your GE. Look below at photo and see if you can find it in these locations. Most likely the defrost timer or adaptive defrost control. But I will not know until you find the model number If it's a Sears model GE the numbers will be different for example 213.0564879
Thanks, Sea Breeze

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Your model TFX20JRBKWWW uses a defrost timer part number WR9X489 located behind the light shield in the fresh foods compartment. (top back area). Just in case you need to know, the defrost heater is a part number WR51X10101 located behind the back wall of the freezer.