Definition
The defrost heater is an electric resistance element that runs alongside or underneath the evaporator coil. Several times a day it energizes briefly to melt off any frost that has accumulated on the coil during normal cooling operation. When the heater fails, frost builds up unchecked and eventually blocks airflow to the rest of the refrigerator.
What It Does
Cold air carries moisture, and as that moisture freezes onto the evaporator coil during cooling cycles, a layer of frost builds up. Too much frost insulates the coil and chokes airflow. The defrost heater activates for about 20–30 minutes every 6–10 hours, raising the coil temperature to about 40–50°F and melting frost into water that drains out through the bottom of the cabinet. The defrost thermostat and a defrost timer or board control when the heater runs.
Where It’s Located
Wrapped around or threaded through the evaporator coil at the back of the freezer compartment. Designs vary: Whirlpool/KitchenAid use a glass-tube heater clipped under the coil; Samsung and LG use an aluminum-sheathed heater integrated into the coil itself; GE often uses a calrod-style heater.
Common Failure Signs
- Thick sheet of frost on the rear freezer wall
- Refrigerator gradually warming up after working fine for years
- Loud noise from the evaporator fan as ice contacts the blade
- Pool of water under the crisper drawers when frost finally melts
- Defrost cycle never runs even though timer/board is calling for it
Typical Replacement Cost
$180–$320 including parts and labor. Glass-tube heaters are $25–$60; sheathed heaters on Samsung and LG run $80–$160 and require more disassembly.
DIY vs Pro
Moderate DIY if you can identify the heater style and have a multimeter to confirm an open circuit. Better as a pro repair because the entire defrost system (heater, thermostat, sensor, board) should be tested together — replacing only the heater when the real failure is the control board wastes money. Book refrigerator repair for full diagnosis.
Need this part replaced? Call (720) 447-8577 for same-day refrigerator repair in the Denver metro area.