Model Number: 650
Brand: Sub Zero
Age: More than 10 years

I have a Subzero 650 fridge. It seems to be running excessively long ~1hr-2hr at a time. Also, I notice that the refrigerator temperature goes all the way down to 30F (my setpoint is at 38F). I've verified the reading w/ a separate thermometer. I've been cleaning the condenser coils pretty regularly. Last year it wasn't able to cool and it was diagnosed to be a leak in the evaporator -- I had the compressor, evaporator, and the capillary tubes replaced during that service visit.

The subzero troubleshooting seems to imply that it could the refrigerator thermistor, but I would think that would cause it to display incorrect temperature as well as have issues w/ cooling.