Where is the defrost timer on model tf20jr

I am not familiar with that particular model, but look around the bottom of the refrigerator first for a small device with a one-way plastic screw. It is about 1/4 inch in diameter and blue, black, or white. As you turn it you will hear it clicking and then when it reaches the defrost part of the turn it will click and the refrigerator compressor will shut off. It's very sensitive, so just a tiny bit more of a turn will turn everything like fan inside freezer back on. Sometimes the defrost timer is next to the t-stat in refrigerator section and in electronic models there is no regular timer-it's solid state. On those any problems with defrosting will usually be a burned out heater or bad defrost terminator or both. Use a meter to find out which. Don't assume the timer is bad-check the heater and defrost terminator (a button t-stat with two or three wires clipped onto side of freezer coils.). Make sure to clean out the coils under refrigerator by vacuuming and a quick spray of water to clean them, then use wet-vac to get up water. Clean fan as well and replace cover on back as you found it or unit will stop working. DrTom4444