A refrigerator defrost timer is a mechanical device that shuts off the appliance's cooling system at regular intervals and turns on the defrost heater for a short time. If the refrigerator is icing up or if it is not cooling, it's possible that either the timer is stuck or it is broken and needs replacing. The timer functions much like a clock and is sometimes called a defrost clock.
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Things you need
- Screwdriver, flat head
- Screwdriver, Phillips head
Look up the defrost timer for your refrigerator's model online on a parts store website. These sites frequently feature photos of parts, which will help you identify your refrigerator's defrost timer.
Unplug the refrigerator.
Find the defrost timer. On most refrigerators or freezers the defrost timer is behind the front grill toe kick near the floor. If you don't find it there, look behind the appliance near the compressor. Or you might find it under a cover plate inside the refrigerator or in the temperature console panel. Expect to remove screws to uncover a protective plate or cover over the defrost timer.
Locate the timer
Locate the advance screw on the defrost timer. It will be either a slot that can be turned with a flathead screw driver or a small knob.
Turn the advance screw clockwise, using the appropriate screwdriver if necessary, until you hear a click.
Plug in the refrigerator.
Wait 30 to 45 minutes and listen to see if the compressor turns on and resumes cooling. If the defrost timer does not advance, it needs to be replaced. If it does advance, you may want to test the switch electrically. Keep in mind, however, that if the refrigerator is icing up and the defrost timer is advancing as it should be, nine times out of ten the problem will be the defrost heater, says appliance service technician Donald Wallgren in Rockford, Ill.
Test to see if the timer is advancing
Unplug the refrigerator again.
Remove the screws that hold the timer in place.
Lift the timer carefully from the appliance, pulling it out far enough to disconnect the wires.
Remove the wires. These typically are harnessed together and can be unplugged as a single unit. If they are not, label the wires for easy reconnection later. Note which terminal connects with the white wire. This is the common terminal.
Set the multitester to X1 ohms.
Touch one of the multitester probes to the common terminal (the one that connected to the white wire.) It may be labelled with a "3" or a "C".
While holding the other probe to the common terminal, touch the other multitester probe to each of the timer's three remaining terminals, one at a time. One or two of these terminals, when paired with the common terminal, should result in a reading of zero or nearly zero ohms. This indicates continuity. The third terminal, when paired with the common terminal, should produce a reading of infinity, which indicates no continuity.
Locate the timer switch on the defrost timer. Turn it clockwise until it clicks.
Retest the timer as in Step 7. The pair of terminals that read infinity in the previous test now should read zero, indicating continuity. The pair or pairs that read zero previously now should read infinity, indicating no continuity.
If the defrost timer fails to pass this test, it should be replaced.
Test the defrost timer electrically
Tips and warnings
- If the refrigerator is icing up and the defrost timer is advancing properly, you may prefer to check that the defrost heater is working first before pulling out the defrost timer to test it with a multitester. The defrost heater will more likely be the problem.
- In older refrigerator models, the timer is most likely located behind the front grill toe kick. In newer models, it is more likely to be inside the temperature control panel.
- Use safety glasses to avoid eye injury when working with tools.
- Tie back hair and avoid wearing loose clothing, which can interfere visually or get caught or tangled when working on appliances.
- Always unplug an appliance before troubleshooting.
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