Quick answer: To test a fridge defrost timer, unplug the fridge, find the timer and disconnect its wires. Use a multimeter to check continuity from the common terminal to each other terminal, advance the timer by hand until it clicks, then test again. A working timer's contacts switch. If they do not, the timer has failed.
What a fridge defrost timer does
A frost-free fridge freezes moisture onto its evaporator coil as it cools. A defrost timer is a small motor-driven switch that interrupts cooling at set intervals and powers the defrost heater so the frost melts and drains away. A defrost thermostat then ends the heating, and the timer returns the fridge to cooling.
If the timer sticks, the heater never switches on, frost builds up, and the fridge warms up even though the freezer may still feel cold.
Signs your defrost timer may have failed
- Thick frost or ice on the back wall of the freezer.
- The freezer is cold but the fridge section is warm.
- The fridge runs without ever starting a defrost cycle.
- The problem returns a few days after you defrost the freezer by hand.
These signs also point to a failed defrost heater or defrost thermostat. See our guides on a freezer not defrosting and a fridge not cooling while the freezer works.
Before you start
- Switch off and unplug the fridge. Do not measure on a live circuit.
- Check you have a mechanical timer. Many newer fridges use an electronic control board instead, and this test does not apply.
- Find your wiring diagram. It is often on the back panel or inside the control box. Terminal numbers vary between makers.
- Take a photo of the wiring before you disconnect anything.
How to test a fridge defrost timer, step by step
- Find the timer. It is often in the control panel behind the temperature dial, behind the kickplate, or near the compressor.
- Remove the timer and disconnect its wires. Disconnect at least one side so you do not read a parallel path through other parts.
- Identify the common terminal. It is often marked 3 or C. Confirm it on your wiring diagram.
- Measure with the timer in its starting position. Set your multimeter to continuity or low ohms. Touch one probe to the common terminal and the other to each remaining terminal in turn. Note which pairs show continuity and which show an open circuit.
- Advance the timer by hand. Turn the timer's knob or slotted screw until you hear a click, then repeat step 4. Pairs that had continuity should now be open, and pairs that were open should now show continuity.
Result: if the contacts switch at the click, the timer is switching. If nothing changes, or the timer will not advance, replace it. Because terminal patterns differ between models, always compare your readings with your wiring diagram.
Defrost timer, heater or thermostat: which part has failed?
| Part | What it does | Quick test |
|---|---|---|
| Defrost timer | Starts the defrost cycle | Contacts should switch when advanced by hand |
| Defrost heater | Melts the frost | Continuity with the fridge unplugged. See our heater test guide |
| Defrost thermostat | Ends the defrost cycle | Continuity when cold, open when warm |
Always test the heater and thermostat as well. A good timer will not fix a burnt-out heater, and a new heater will not help if the timer never starts a cycle.
When to replace the timer
Replace the timer if its contacts do not switch, the motor does not advance, or it is visibly damaged. Match the old timer's markings and your model number before ordering. Fitting should be done by a licensed refrigeration mechanic or electrician because the timer controls 240V circuits.
Defrost timers we stock
- Defrost timer for Westinghouse fridges (RJ390P, RJ390M, RJ280M, SR300A-R, N476C), $12.20.
- Defrost timer 6hr 21min for fridges and freezers, $13.80. Check the markings on your old timer before ordering.
Browse all defrost timers and thermostats and Westinghouse fridge parts. Not sure what fits? Use Find Your Part and send your model number. Orders placed by 6pm Sydney time ship the same business day from Colebee, NSW.
Defrost timer FAQs
What does a fridge defrost timer do?
A mechanical defrost timer switches a frost-free fridge between cooling and defrost. At set intervals it turns off the cooling circuit and sends power to the defrost heater, so frost melts off the evaporator coil.
How do I know if my defrost timer has failed?
Typical signs are heavy ice on the freezer back wall, a warm fridge section with a cold freezer, or a freezer that never seems to start a defrost. The timer, heater and defrost thermostat can all cause these signs, so test all three.
Can I test a defrost timer with a multimeter?
Yes. With the fridge unplugged and the timer disconnected, measure continuity between the common terminal and the other terminals, then advance the timer by hand and measure again. The contacts should switch. Use the wiring diagram for your model.
Where is the defrost timer in my fridge?
It is often in the control panel behind the temperature dial, behind the kickplate or near the compressor at the back. Locations vary by model, so check your manual or model number.
Does every fridge have a defrost timer?
No. Many newer fridges control defrost with an electronic board instead of a mechanical timer. If you cannot find a timer, this test does not apply to your fridge.
Can I replace a defrost timer myself?
Defrost timers are 240V parts and wiring mistakes can damage the fridge, so fitting should be done by a licensed refrigeration mechanic or electrician. Photograph the wiring before disconnecting anything.