Definition
The defrost thermostat (also called a defrost bimetal or defrost limit) is a small temperature-sensitive switch clipped to the evaporator coil. It closes the circuit to the defrost heater only when the coil is cold enough (typically below 20°F) and opens again once the coil warms to around 40–60°F. This prevents the heater from running needlessly and prevents overheating during the defrost cycle.
What It Does
Every 6–10 hours the defrost timer or main control board calls for a defrost cycle. Current is routed to the defrost heater, but only through the defrost thermostat — if the coil is already warm, the thermostat is open and no heat is applied. As soon as the coil is cool again the thermostat closes, ready for the next defrost. A failed thermostat that is stuck open will let frost build up on the coil indefinitely and choke off airflow.
Where It’s Located
Clipped directly onto the metal tubing of the evaporator coil, behind the freezer rear panel. Brand examples: Whirlpool, KitchenAid, and Maytag use the WP2188819 series on many models. Samsung and LG use a similar disc-style bimetal mounted with a single clip.
Common Failure Signs
- Heavy frost buildup on the rear freezer wall
- Refrigerator section warming gradually over 24–48 hours
- Evaporator fan noise that gets quieter or stops as ice blocks the blade
- Defrost heater tests good but never runs
- Frost returns within days of being manually thawed
Typical Replacement Cost
$140–$240 including parts and labor. The part itself is only $15–$35, but accessing it requires emptying the freezer and removing the rear panel.
DIY vs Pro
DIY possible with a multimeter and a few hours. The repair is moderate difficulty because the coil must be thawed first if heavily iced. Many homeowners prefer to call a tech to handle defrost-system diagnosis as a whole, since the thermostat, heater, and control board all interact. Book refrigerator repair for a full defrost diagnosis.
Need this part replaced? Call (720) 447-8577 for same-day refrigerator repair in the Denver metro area.