, the customer began to notice odd behavior out of this unit for the past couple weeks. Sometimes the unit would cool just fine and make all the normal sounds he was familiar with. And other times, the unit would start to warm up and make no noise at all. After a little investigation, he noticed if the temperature control was rotated from one extreme to the other, often everything would turn back on and begin to cool. But after throwing away enough food that had gone bad, it was time to get this intermittent problem fixed.
The temperature on this unit is regulated by a mechanical capillary thermostat often referred to as a cold control. These use a capillary tube which contains a temperature sensitive liquid that will expand and contract with a change in temperature. This movement is translated by a bellows to a spring loaded switch armature that connects to a set of electrical contacts used turn the refrigerators compressor on and off.
Temperature adjustments are made by changing the spring tension of the armature requiring more force to move the armature. This requires the belows to expand or contract more in order to open or close the contacts. So as the temperature inside the refrigerator increases, the capillary liquid will expand pushing the bellows and the armature with more force until it is warm enough to overcome the resistance of the spring and close the circuit starting the compressor.
When I arrived to this refrigerator, it was not cooling and after the customer explained what had been going on and how he had been able to make it limp along, I was sure the thermostat was the problem. Once the panel cover was removed, I used my meter to do a voltage check across the two wire terminals and found source voltage which told me the switch contacts were open. I then removed the thermostat from the housing and did a continuity check and found an open circuit no matter the position of the temperature selector knob. With source voltage present and an open circuit, it looks like I found the problem.
Installed a new thermostat into the control housing and while being careful of the placement of the capillary tube, put everything back together. If you change your own capillary thermostat, make sure the capillary tube is placed back where the old one came out and nothing is covering the sensor bulb at the end. Improper placement can lead to significant temperature changes inside the unit. With a new thermostat in place, this refrigerator is now cooling properly again, and the customer can even select the proper temperature.