The defrost heater is an electric element inside or beside the evaporator coil that melts frost during the defrost cycle. When it fails, ice builds up and does not clear, the coil blocks and the box warms. A technician tests it with a meter and replaces failed elements.
In electric defrost freezers, heaters do the hard work of melting ice several times a day. They are exposed to moisture, thermal cycling and sometimes physical damage, so failures are not unusual.
What it does
During defrost the compressor and evaporator fans stop and current flows through heater rods placed between the coil fins or under the pan. The heat melts frost, which drips into the drain pan. A termination switch or timer ends the cycle. Freezer drain lines often have their own heater to prevent freezing.
Signs it is failing
- Ice remains on part of the coil after defrost.
- Ice builds in a pattern that never clears.
- Water at the drain pan is low or absent.
- Breaker trips during defrost.
- Box temperature climbs over days.
- Defrost runs to its maximum time.
Common causes of failure
| Cause | What happens |
|---|---|
| Burnt-out element | Open circuit, no heat |
| Damaged insulation | Moisture causes shorts and trips |
| Loose or corroded wiring | No power to the element |
| Failed relay or contactor | Power never reaches the heater |
| Mechanical damage | Bent or crushed while chipping ice |
What you can safely check
- Look at the ice. Does it clear evenly or in patches?
- Watch a defrost. Note whether water runs into the pan.
- Note breaker trips. Do they occur at defrost times?
- Do not chip ice. Damage to heaters is a common result.
This part is on live power. Do not open the electrical box, bridge terminals or reset repeatedly. Only a qualified technician should test or replace it.
What a technician does
- Tests each heater with a meter for continuity and ground faults.
- Checks relays, wiring and the termination switch.
- Replaces failed elements as a set when needed.
- Clears ice safely after repair.
- Confirms amp draw matches the rating.
Keeping it healthy
- Do not chip or scrape ice from the coil.
- Report breaker trips at defrost times.
- Keep the drain pan and line clear.
- Include heaters in yearly service.
If one heater has burnt out, others of the same age may not be far behind. Ask the technician whether replacing the set makes sense.
When to call for service
Call if ice remains after defrost, if the breaker trips at defrost times or if the coil is blocked. Do not chip the ice. If food is at risk, move it to another freezer while waiting, and record the temperature and time.
Repair or replace
Heaters are replaced, and the job needs some access to the coil. Repeated failures point to water getting in, poor drainage or damaged wiring. See the termination switch page and freezer not freezing for related issues.
Related reading: the parts and components guide, ice on floor or ceiling and the troubleshooting guide.
Questions about this part
Can I defrost by hand instead?
Occasionally in an emergency, but see the safety guidance on hot water and heat guns.
Why does the breaker trip during defrost?
Heaters draw high current. A shorted element can trip it.
Do coolers have defrost heaters?
Some do. Many defrost using off-cycle air.