This is perhaps one of the easiest refrigerator problems to troubleshoot and to repair. A refrigerator that runs continuously and freezes everything in both the refrigerator and freezer compartment is pointing the finger at the main temperature controls. You can locate the problem and repair it with nothing more than a few simple hand tools and a DMM (Digital Multimeter).
Schematic Versus Pictorial Diagrams
Two of the most important tools in your tool kit when it comes to troubleshooting any home appliance are provided free by the appliance manufacturer. On the back of every modern refrigerator you will find a pictorial wiring diagram and a schematic wiring diagram. The pictorial diagram shows the refrigerator's components as they actually look. The schematic diagram represents the components using schematic symbols. By comparing the pictorial diagram to the schematic diagram, you will learn what the schematic symbols mean. Take the time now to learn the symbols because they will be invaluable to you in the future.
Locate the Thermostat's Wiring Harness Connector
Unplug the refrigerator from the wall receptacle before continuing troubleshooting. Using the pictorial and schematic diagrams as reference, locate the wiring harness from the thermostatic control and unplug it from the terminal board in the compressor compartment at the base of the refrigerator cabinet. If you have an older style refrigerator, the wires may be equipped with individual push-on terminal. In some cases, with older refrigerators, you may have to remove the thermostat from the refrigerator to test it properly.
Testing the Thermostat for Electrical Problems
Again using the wiring diagrams, determine which of the wires coming from the thermostat supply the power to the compressor motor's start relay switch. To check the thermostat, you will need to take a continuity reading through the thermostat's main contacts. To do this, set the function on your DMM to the R X 1 function, insert the test probes into the holes on the harness plug associated with those wires and rotate the knob on the thermostat through its full range. In the thermostat's “OFF” position, the meter's LCD should display an “O.L.” and then, as you rotate the knob clockwise, the LCD should display a “0.000” if the thermostat is functioning properly, electrically. If you get a “0.000” reading even in the “OFF” position, the thermostats internal contacts are stuck in the closed position, and you need to replace the thermostat.
Defective Temperature Sensing Tube
If the thermostatic control checks out electrically, the problem lies with its temperature sensing tube or bulb. This tube contains a gas which condenses as it get cold. As the gas volume decreases, the spring loaded contacts open, shutting the compressor off. There is no way to recharge the sensing tube once it has lost its charge, so you will have to replace the complete thermostat control.
Buying Replacement Parts
Buying the correct replacement parts for any appliance can be tricky, especially for the inexperienced DIY person. The best way to make sure you get the right part for your appliance is to take the old part, along with the make, model and serial numbers of your appliance, to the appliance parts supplier with you so that the parts counter person can compare the old part to the new part.