Quick answer: To test a fridge defrost heater, unplug the fridge, remove the freezer back panel, disconnect the heater and measure across its two terminals with a multimeter set to ohms (Ω). An Australian 240V fridge defrost heater should usually read about 100–200 Ω. A reading of OL (open) means the heater has failed and needs replacing.
If your freezer back wall is covered in ice, or your fridge is warm while the freezer still feels cold, the defrost heater is one of the first parts to check. This guide shows you how to find it, test it and work out whether it's the heater, the defrost thermostat or something else. It also covers the problem most guides skip: a defrost heater that keeps tripping your safety switch.
What a Fridge Defrost Heater Does
In a frost-free fridge, cold air is made by an evaporator coil behind the freezer back panel. Frost slowly builds up on that coil. A few times a day the fridge stops cooling and switches on the fridge defrost heater, a heating element fixed to the coil, to melt the frost. The water drains away and cooling starts again.
The heater is controlled by a defrost timer (or the control board) and protected by a defrost thermostat, which switches the heater off once the coil warms up. If any of these three parts fails, frost keeps building until air can't flow.
Fridge Defrost Heater Not Working: Common Signs
- Ice or frost on the freezer back panel, often thickest at the top or around the air vents.
- Fridge warm, freezer still cold: ice blocks the airflow from the freezer into the fridge.
- Water leaking into the crisper or onto the floor when ice melts unevenly.
- Clicking or scraping noise from the freezer fan as the blade hits ice.
- Fridge works again after a manual defrost, then the problem returns within days. This is a classic sign of a failed defrost system.
If the coil is evenly frosted all over, suspect the defrost heater, thermostat or timer. If frost only covers part of the coil, it can point to a refrigerant problem instead, which needs a licensed refrigeration mechanic.
Fridge Defrost Heater Location
The defrost heater is always attached to the evaporator coil, so where it sits depends on the type of fridge:
| Fridge type | Where to find the defrost heater |
|---|---|
| Top mount | Behind the back panel inside the freezer, at the top |
| Bottom mount | Behind the rear panel of the freezer drawer, sometimes under the freezer floor |
| Side-by-side | Behind the back panel on the freezer side |
| French door | Behind the freezer drawer rear panel, at the bottom |
You'll see either a metal tube (Calrod-style) element woven through or under the coil, or a glass tube heater running under the coil. The defrost thermostat is usually clipped to the coil pipe nearby.
What You Need
- A digital multimeter
- A screwdriver or nut driver (often Phillips or 1/4" hex)
- Towels and a container for melting ice
- A cooler box for your food
How to Test a Fridge Defrost Heater With a Multimeter
- Turn off and unplug the fridge. Don't rely on the fridge's own power button; the defrost circuit is 240V.
- Empty the freezer and remove the shelves, drawers and ice maker if fitted.
- Remove the freezer back panel by undoing its screws. If it's frozen in place, let the ice melt first rather than forcing it.
- Find the heater terminals: two wires with push-on connectors at each end of the element.
- Disconnect both wires. Testing with the wiring still connected can give a false reading through other parts.
- Set the multimeter to ohms (Ω), on the 200 Ω or 2 kΩ range, or auto-range.
- Touch one probe to each terminal and read the display.
- Compare your reading with the table below or with the heater's wattage.
What the Reading Means
| Reading | What it means | What to do |
|---|---|---|
| About 100–200 Ω (close to expected value) | Heater is good | Test the defrost thermostat next |
| OL, 1 or infinite | Element is open (burnt out) | Replace the heater |
| Close to 0 Ω | Element is shorted | Replace the heater |
Fridge Defrost Heater Resistance (Ohms) for 240V Heaters
Many online guides say a good defrost heater reads 10–150 Ω. Those figures are for 120V American fridges. Australian fridges run on 240V, so the same wattage gives a higher resistance. You can work out the expected value with a simple formula:
Resistance (Ω) = 240 × 240 ÷ heater wattage
Your reading should be within about 10% of this figure. Here are the expected values for the heaters we stock:
| Heater | Wattage | Expected resistance (approx.) |
|---|---|---|
| Westinghouse / Kelvinator RF116 | 350W | 165 Ω |
| Westinghouse / Kelvinator RF153 | 450W | 128 Ω |
| Westinghouse side-by-side (RS643V, SE114) | 450W | 128 Ω |
| Generic heater for Fisher & Paykel 322W | 322W | 179 Ω |
| Generic heater for Fisher & Paykel 355W | 355W | 162 Ω |
Resistance changes slightly with temperature, so test the heater at room temperature where you can.
Fridge Defrost Heater Tripping Breaker or Safety Switch
If your fridge trips the safety switch (RCD) or breaker a few hours after it's plugged in, the defrost heater is a common cause. The trip happens when the defrost cycle starts, which is why the fridge seems fine at first.
Why it happens: the heater's outer sheath or glass tube cracks, moisture gets inside, and current leaks to earth. The heater may still read a normal resistance between its two terminals, so a basic ohms test won't always find this fault.
How to check it:
- With the fridge unplugged and the heater disconnected, set your multimeter to its highest resistance range.
- Touch one probe to a heater terminal and the other to the metal sheath, mounting bracket or the fridge's earth point.
- Repeat for the other terminal.
- Any reading other than OL (open) means current is leaking to earth. Replace the heater.
A multimeter can miss small leaks that only show up at full voltage. An electrician can confirm the fault with an insulation resistance tester. Also check for melted connectors, damaged wiring near the heater and water dripping onto the element. Never bypass or keep resetting a safety switch. It's tripping to protect you.
Heater Tests OK? Check These Next
- Defrost thermostat: it should read close to 0 Ω (closed) when cold, below about −5 °C. Test it while it's still frozen or after chilling it in the freezer. If it reads open when cold, replace it.
- Defrost timer: on mechanical-timer fridges, turn the timer slowly with a screwdriver until it clicks into defrost. The compressor should stop and the heater should warm the coil within about 15–20 minutes. If not, the timer or wiring may be faulty.
- Control board: on electronic fridges, the board runs the defrost cycle. Check for an error code in your user manual, or have a technician diagnose it.
Shop defrost thermostats and timers.
Replacing a Fridge Defrost Heater
To replace the heater, match the wattage, length, voltage and terminal type of your old part, or use the part number printed on it. Unclip the old element, fit the new one in the same position, reconnect the wires and refit the back panel. Because it's a 240V part, fridge defrost heater replacement should be done by a licensed refrigeration mechanic or electrician.
A new heater is a low-cost repair compared with replacing the fridge. If your thermostat is more than a few years old, replacing it at the same time is good practice.
Fridge Defrost Heater FAQs
How do I know if my fridge defrost heater is not working?
The most common sign is frost or ice on the freezer back panel, often with the fridge section running warm. A multimeter reading of OL across the heater terminals confirms it has failed.
What should a fridge defrost heater read in ohms?
Most Australian 240V defrost heaters read about 100–200 Ω. Divide 57,600 by the heater's wattage for the exact expected value. For example, a 350W heater should read about 165 Ω.
Why does my fridge defrost heater keep tripping the breaker?
Usually because the heater's sheath or glass tube is cracked and moisture is leaking current to earth. Test between each terminal and the metal sheath. Any reading other than open means the heater should be replaced.
Where is the defrost heater in my fridge?
It's attached to the evaporator coil behind the freezer back panel. In top mount fridges that's at the top of the freezer. In bottom mount and French door fridges it's behind the freezer drawer.
Can a fridge work without a defrost heater?
Only for a short time. Without it, frost builds up on the coil until air can't flow and the fridge stops cooling properly. A manual defrost is a temporary fix only.
Should I replace the defrost thermostat with the heater?
It's not required, but many technicians do. The thermostat is cheap and commonly fails alongside the heater, so replacing both saves a second repair.
Shop Fridge Defrost Heaters
Tested your heater and found it's failed? Order a replacement from Fast Fridge Spares. Orders placed by 6pm are dispatched the same business day from Colebee, NSW, with most arriving in 1–2 business days.
- All fridge defrost heaters
- Westinghouse / Kelvinator RF116 defrost element 350W
- Westinghouse / Kelvinator RF153 defrost element 450W
- Westinghouse side-by-side defrost element 450W
- Defrost element for Fisher & Paykel 322W
- Defrost element for Fisher & Paykel 355W
- Defrost thermostats and timers
Not sure which heater fits your fridge? Send us your model number through our Find Your Part page.
Safety note: this guide is general information. Defrost heaters run on 240V mains power. Always unplug the fridge before testing, and have electrical repairs done by a licensed professional.