Hi, this is Wayne from Sears PartsDirect. Today, we're going to talk about refrigerator thermistor troubleshooting. The thermistor senses the temperature inside the refrigerator. The electronic control board monitors the thermistor and controls refrigerator temperature based on thermistor signals. So, if your refrigerator’s not cooling, which one’s the problem?
Check thermistor for damage
Let’s check the thermistor first. For safety, unplug the refrigerator. Drop down the control box in the ceiling of the refrigerator to access the thermistor. Examine the thermistor's wire harness for damage or loose connections. If the wiring harness looks okay, let’s check the resistance of the thermistor using a multimeter.
Remove the thermistor and put the meter leads on the two white wires. The tech sheet for your refrigerator includes a temperature/resistance chart for the thermistor. You can usually find the tech sheet inside the refrigerator, stored behind the bottom front grill. Refer to this chart for the expected resistance readings for your model.
On this model, at a room temperature of 72 degrees, you should measure around 11,000 ohms of resistance through the thermistor. Place the thermistor in a cup of ice water and you should measure around 27,000 ohms of resistance because the water temperature is around 32 degrees. Replace the thermistor if the resistance readings are off by more than 10 percent. This video will show you how.
Inspect wiring harness
If the thermistor resistance checks okay, we know it’s not the thermistor. We still have 2 possible failures: the wire harness or the electronic control board. Let’s check the thermistor wiring harness. Plug the thermistor back in. Remove the 13-pin connector from the electronic control board.
Put one meter lead on the gray and black wire and the other on the red wire. You should measure the same resistance that you measured directly at the thermistor at room temperature. If the reading is different, replace the wire harness or repair the thermistor wires.
Confirm electronic control board failure
If the thermistor and the thermistor's wire harness are both working, the problem is likely in the electronic control board because we've eliminated the other possible causes of inaccurate temperature measurement. Before you buy a control board, I recommend that you make sure the compressor and evaporator fan are working.
The electronic control board operates those components based on the thermistor reading. A bad evaporator fan or failed compressor can mimic a thermistor problem. To confirm an electronic control board failure, you’ll need to turn on the compressor and evaporator fan in the diagnostic test mode.
First, reassemble the control box and then plug the refrigerator back in. Within two seconds, press the light switch 3 times and then press and hold it a 4th time until you hear a long beep. You're now in the test mode. If this doesn’t work on your model, check your tech sheet for instructions. Press the door switch twice to start the compressor. The control beeps twice and then you should hear the compressor start. To check the fan, press the door switch twice WITHIN 2 SECONDS and wait for the 2 beeps. Repeat this step two more times. The control beeps twice and then starts the evaporator fan.
If both the fan and the compressor run in the diagnostic test mode, you'll need to replace the electronic control board because we've eliminated the other possible causes of inaccurate temperature detection and control. Here's a video that shows how to replace the electronic control board.
Other possible problems
If the fan or compressor doesn't run, you can learn how to troubleshoot the evaporator fan and compressor in these videos.
Well I hope this video helps you out today. Be sure to check out our other videos here on the Sears PartsDirect YouTube Channel, and don't forget to subscribe.