I'm not sure why you didn't get my previous reply, but I am extremely pleased with the information you provided me. I purchased the replacement heater and replaced it this past weekend. I used a blow dryer to melt the ice that had built up around the coils to expose the defrost heater. After the water drained, swapping out the unit was fairly straight forward. The refrigerator and furnace have been working fine ever since.
Thank you again for your assistance.
After two weeks of running fine, my refrigerator is exhibiting the same problem as before: ice build up in freezer on back wall, inability for refrigerator to stay cold, etc. Could this be the defrost heater tube again or should I be looking at something else?
OK. I took freezer apart again and exposed the coils. After the unit defrosted all day, I was able to test the defrost heater that I installed 2 weeks ago. It has between 30-40 ohms resistance, so I don't think that is the problem. I found the round defrost thermostat with two wires sticking out of it. I don't have clips to connect to the wires, so I just held the probes on either side of the 1" round device. Am I checking this correctly? It gives me 0.00 on my multimeter.
I only replaced the defrost heater so far. I haven't replaced the thermostat yet. Your explanation does make sense. The thermostat is open because I defrosted the freezer and it is above 32 degrees. I would need to plug in the fridge to get the freezer below freezing and then test thermostat again. If it is still open, then I would need to replace it, correct? If it has resistance, then by process of elimination, it would have to be the defrost timer.
I will let you know about the thermostat after it freezes. Thanks Tyler.