Quick answer: A frost-free fridge melts the frost off its evaporator coil with a heater. A timer (or control board) starts the defrost, the heater melts the frost, and a thermostat ends the heating. If any one of these fails, frost builds up and the fridge warms. Test the heater, timer and thermostat before you buy a part.
How a frost-free fridge defrosts
As a frost-free fridge cools, moisture freezes onto the evaporator coil behind the freezer back panel. If it were left alone, the frost would block the airflow. So the fridge runs a short defrost cycle several times a day.
- Cooling stops. A timer or control board interrupts the cooling cycle at set intervals.
- The heater switches on. The defrost heater warms the evaporator coil and melts the frost.
- The water drains away. Meltwater runs out through the drain.
- The thermostat ends the cycle. When the coil warms up, the defrost thermostat opens and the heater switches off.
- Cooling restarts.
The parts of the defrost system
| Part | Job | Our test guide |
|---|---|---|
| Defrost timer | Starts the defrost cycle | How to test a defrost timer |
| Defrost heater | Melts the frost | How to test a defrost heater |
| Defrost thermostat | Ends the cycle | How to test a defrost thermostat |
| Evaporator fan | Moves cold air through the fridge | Evaporator fan not working |
| Drain | Carries meltwater away | Check it is clear of ice and debris |
| Control board (some fridges) | Runs defrost instead of a timer | Not sold by us |
Signs the defrost system has failed
- Thick frost or ice on the freezer back wall.
- The freezer is cold but the fridge section is warm.
- Weak airflow from the vents.
- The fridge works for a few days after a manual defrost, then warms up again.
- Water leaking onto the floor or into the crisper.
Our guides on a freezer not defrosting and a fridge not cooling but freezer working cover these signs in detail.
What to test, in order
- Look at the ice. Frost over the evaporator points to the defrost system. If ice touches the fan blade, defrost the fridge fully first.
- Test the heater. With the fridge unplugged, check continuity. It is quick and a very common failure.
- Test the thermostat. It should be open when warm and conducting when cold.
- Test the timer. If your fridge has one, its contacts should switch when advanced by hand.
- Check the drain and the fan. Make sure the drain is clear and the evaporator fan turns.
Replace only what failed. A new timer will not fix a burnt-out heater, and a new heater will not help if the thermostat never lets it run.
Defrost parts we stock
| Part | Details | Price (AUD) |
|---|---|---|
| RF116 defrost heater | 350W, 440mm, Westinghouse and Kelvinator | $28.50 |
| RF153 defrost heater | 450W, 520mm, Westinghouse and Kelvinator | $29.50 |
| SE114 side-by-side heater | 450W, for RS643V and RS662V | $29.00 |
| Fisher & Paykel 322W heater | 46cm, generic, no plug | $28.00 |
| Fisher & Paykel 355W heater | 57cm, generic | $28.00 |
| Defrost timer for Westinghouse | RJ390P, RJ390M, RJ280M, SR300A-R, N476C | $12.20 |
| Defrost timer 6hr 21min | For fridges and freezers | $13.80 |
| Defrost thermostat, Klixon type | 240V, SL5708, L50-25F, RF027M | $13.50 |
These are replacement parts, not genuine branded parts. Match the part number, wattage and length on your old part before you order. Browse fridge defrost heaters, defrost timers and thermostats, Westinghouse fridge parts and Fisher & Paykel fridge parts. Not sure what fits? Use Find Your Part or read how to find your fridge model number. Orders placed by 6pm Sydney time ship the same business day from Colebee, NSW.
Safety
Switch off and unplug the fridge before testing. Defrost parts are 240V, so fitting should be done by a licensed refrigeration mechanic or electrician.
Defrost system FAQs
How does a frost-free fridge defrost?
A timer or control board stops the cooling cycle at set intervals and powers a heater on the evaporator coil. The heater melts the frost, the water drains away, and a thermostat ends the heating before cooling restarts.
Which part fails most often in a defrost system?
Any of the heater, timer or thermostat can fail, and a fault in one looks like a fault in another. The only reliable way to find the cause is to test all three, starting with the heater because it is quick to test.
Why is there ice only on the freezer back wall?
Ice over the evaporator cover on the freezer back wall points to the defrost system not melting frost. The heater, timer, thermostat or a drain problem can cause it. Test the defrost parts before replacing the fan or the fridge.
Does every fridge have a defrost timer?
No. Many newer fridges use an electronic control board to run the defrost cycle. If you cannot find a mechanical timer, the timer test does not apply. We do not sell control boards.
Should I replace the heater, timer and thermostat together?
Not by default. Test each part and replace only the one that has failed. If one part has burnt out and the others are old, replacing the thermostat at the same time can make sense.
Can I fix a defrost fault myself?
Testing is safe with the fridge unplugged, but the defrost parts are 240V and fitting should be done by a licensed refrigeration mechanic or electrician.