FRT18G4AWC Defroster Thermostat – What Fixes Defrost System Problems
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Understanding the Problem
Brief explanation: The defroster thermostat (also called the defrost limiter or defrost sensor/bi-metal thermostat) on your Frigidaire FRT18G4AWC monitors the evaporator coil temperature and closes to allow the defrost heater to run when the coil is cold. If this thermostat fails open or doesn't close at the correct temperature, the defrost heater won't run and frost/ice will build on the evaporator. That leads to poor cooling, excessive frost in the freezer, and a refrigerator that cycles on and off abnormally. Step-by-step diagnostic and repair instructions: 1) Confirm the symptom: excessive frost buildup on evaporator, poor cooling, freezer needing manual defrost, or frost blocking airflow to fridge section. Also note long run times or compressor running but temperatures climbing. 2) Unplug refrigerator: always cut power at the wall before inspecting electrical components. 3) Remove/freezer evaporator access: typically remove food, shelves, and the rear freezer panel to expose the evaporator and defrost components (heater and thermostat). Keep screws and panels organized. 4) Locate the defrost thermostat: it is a small round or rectangular bi-metal device clamped to the evaporator coil or mounted nearby with two wires attached. It may be inside a rubber boot on the coil or clipped directly to the tubing. 5) Visual inspection: look for burned, corroded, or disconnected wires, or a cracked rubber boot — replace if damaged. 6) Test thermostat cold/hot behavior (multimeter continuity): a. Remove one wire connector (so you're testing only the thermostat). b. With refrigerator powered off, place the thermostat in an ice-water slurry (or a sealed bag of ice pressed to the sensor) to force it to cold state. A good thermostat should show continuity (closed) at cold temperatures (typically around 0°C / 32°F or below depending on design). c. At room temperature it may be open. If it never shows continuity when cold, it's failed open and should be replaced. 7) Test in-system during defrost cycle: if you can safely access and the defrost timer or control can be set to defrost, enter a manual defrost and measure whether the thermostat closes and allows current to the defrost heater. If the heater gets power but doesn't heat, test the heater element separately for continuity. 8) Replace thermostat if faulty: obtain correct replacement (see parts list). Replacement steps: a. Unplug refrigerator. b. Remove evaporator access panel and free up thermostat leads. c. Unclip the old thermostat from the coil (note orientation and mounting). If rubber boot used, remove boot carefully. d. Disconnect terminals and swap in new thermostat; secure any rubber boot and clip to coil in the same position. e. Reassemble paneling and restore power. 9) Verify operation: allow refrigerator to run and/or force a defrost cycle. Confirm frost clears from evaporator and that normal cooling resumes. Monitor for a couple of cycles (24–48 hours) to ensure frost doesn't return. 10) If still frosting: test defrost heater for continuity and the defrost control/timer or main control board for proper defrost initiation. A working thermostat and heater still need a functioning defrost timer/control to run defrost cycles. Safety note: Work on appliances only if you are comfortable with basic electrical safety. Always unplug the unit before any disassembly. Use insulated tools, avoid contact with sharp sheet metal, and wear gloves and eye protection. If unsure, hire a qualified appliance technician.
Common Symptoms
Excessive ice/frost on evaporator, poor cooling in fridge/freezer, long run times, manual defrost required frequently, or defrost heater never appears to run.
Common Causes
- Defrost thermostat has failed open and won't close at cold temperature
- Wiring to thermostat is corroded, disconnected, or shorted
- Defrost heater or defrost control fails (thermostat fine but system never enters defrost)
- Thermostat mounted incorrectly or rubber boot damaged causing incorrect temperature sensing
Popular Parts That Fix This Problem
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Helpful Repair Tip
To confirm the thermostat is bad, remove it and hold it in an ice-water bath — if it doesn't show continuity on a multimeter when cold, replace it.
Frequently Asked Questions
How do I test the defrost thermostat with a multimeter?
Disconnect power, remove the thermostat from the evaporator, and disconnect one wire. At room temp the thermostat may be open; place it in an ice-water slurry (or press a bag of ice against the sensor) and check continuity. A good thermostat should show continuity (near 0 ohms) when cold. No continuity when cold means the thermostat is defective.
Can I bypass the defrost thermostat to restore cooling?
Do not bypass the defrost thermostat as a permanent fix. Bypassing can allow the defrost heater to run uncontrolled, risking melted insulation, overheating, or electrical hazard. Only replace the defective thermostat with a correct OEM or compatible replacement. If you're unsure, call a qualified technician.
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