Hi there, hoping you can help!

We have a Kenmore model 106.50522101. Our problem is that the fridge side is way too warm (45-50) and the freezer is way too cold (-10 -- -20) The freezer has frost and ice buildup everywhere - there's a layer of ice on the bottom floor, and "snow" (as the kids call it) everywhere.

One time I found that a vent on the bottom left of the fridge was blocked with ice. I defrosted it with a hair dryer and it seemed to be a drain tunnel of some sort. After I defrosted that, and also the ice around a couple vents leading into the fridge, the temp dropped to 36 in the fridge. However, after a week or 2 it went warm again and now the hair dryer trick won't work.

We tried the diagnostics steps today. We advanced the timer and the defrost cycle turned on, but we never heard sizzling. (unless it's really really quiet?) We also found the defrost heater and it didn't appear to be on.

So next we unplugged the fridge and checked for continuity on the defrost heater. We also noticed that the heater was cold even though the defrost cycle had just been on. The analog multimeter read zero, so we're assuming that means there *is* continuity, so the next step is the defrost thermostat?

However, at this point we've noticed a few more things:

1) The drain plug under the evaporator coils is completely plugged with ice. But could this be a cause of, or a symptom of, our problem?

2) The evaporator coils are not covered in ice. However my husband is saying that he's almost positive there's ice *behind* them, if that's possible?

Would either of those things cause the defrost heater not to turn on? Or should I go ahead and just order the defrost thermostat?

This problem all started after the kids left the freezer door open all night one night. (Partially closed over but not sealed) So could it just be ice and frost buildup from that?

Thanks for all your help!!