Frost on the back panel in the freezer indicated that the defrost system was not working. The defrost timer is in the top of the refrigerator compartment near the light and temp control. I looked at the manual advance on the timer noting it's position. I looked a couple hours later and could tell that it was advancing. I advanced it manually and the compressor stopped (now in defrost mode). I advanced it manually 5 minutes later and it started again - therefore the timer was functioning properly. I unplugged frig, opened the back panel in freezer, and by-passed the thermostat (took it out of the circuit to the heating element). I plugged frig back in and advanced the timer to defrost mode. After a couple of minutes I could feel heat from the heating element. By process of elimination, it was the thermostat. I ordered the thermostat. The old thermostat wires had plugs on the end, so I cut the wires off the old thermostat and spliced them on to the new thermostat so I could just plug the new thermostat in to the system. Note: you cannot wire a 2 lead thermostat backwards, so don't worry about which wire goes where. It took a couple hours to figure out how to disassemble and diagnose and 45 minutes to replace the thermostat. Should just need a socket set and wire strippers/crimping tool.