Frigidaire FRT18G4AWC Defrost Thermostat – What Part Fixes Defrost Problems?
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Understanding the Problem
The defrost thermostat (also called a defrost sensor or bi-metal thermal switch) sits on the evaporator coil and senses freezer temperature. During the defrost cycle it allows the heater to get power when the coil is cold and opens when the coil warms, protecting the heater and control. If it fails, the heater may never run during defrost and frost/ice will build on the evaporator causing poor cooling, or it may stick closed and allow improper operation. Step-by-step diagnostic and repair instructions: 1. Verify symptoms: look for thick frost on the back freezer wall or evaporator cover, frozen air channels, long compressor run times, or a warm fresh-food compartment. Confirm there is no obvious blown fuse/failure of the heater first. 2. Unplug the refrigerator or turn off the breaker. Safety first—work only on a de-energized appliance. 3. Empty the freezer section enough to access the rear evaporator cover. Remove shelves and any drawers blocking access. 4. Remove screws and take off the evaporator cover/panel to expose the evaporator coil and defrost components. Note or photograph wiring and component locations for reassembly. 5. Locate the defrost thermostat: it is a small cylindrical or oval bi-metal switch clamped to the evaporator coil or attached by a small clip and has two female connector leads. 6. Test the thermostat with a multimeter set to continuity or ohms: - Put the thermostat in a cold condition (place it in a cup of ice water or leave it in the freezer until it is very cold). In the cold state (below its trip temperature, typically around 0°C to -10°C depending on design) it should show continuity (closed). If it shows open when cold, it is bad. - Warm it with a hairdryer (or allow it to warm to room temperature); the thermostat should open (no continuity) as it warms. If it does not change state, it is failed. 7. Inspect the defrost heater and wiring: if thermostat tests good, check the heater element for continuity and the harness and connectors for damage. If heater is open but thermostat is good, replace the heater instead. 8. Replace the thermostat if failed: - Unplug the fridge. Remove connectors from the old thermostat (note wiring orientation). Remove the mounting clip or adhesive and free the thermostat from the evaporator. - Install the new thermostat in the same location and orientation, secure with the clip so its sensing end contacts the coil. Reconnect the wiring using the same connectors. - Reassemble the evaporator cover, replace shelves/drawers and restore power. 9. Test operation: allow the unit to run and either put it through a forced/advance defrost (using the control board or service mode) or wait for the normal defrost cycle. Verify the heater turns on during defrost and that frost melts off the evaporator. Safety note: Always disconnect power before opening covers or handling electrical connectors. The evaporator fins are sharp—wear gloves. If you are unsure about working with appliance electrical components, contact a qualified technician.
Common Symptoms
Heavy frost/ice buildup on evaporator or freezer back wall, long or continuous compressor run times, poor cooling in refrigerator compartment, no defrost heater operation during defrost cycle.
Common Causes
- Failed defrost thermostat (open when it should be closed)
- Faulty defrost heater (open) while thermostat functions
- Defrost control (timer or electronic board) or wiring issue preventing power to the heater
Popular Parts That Fix This Problem
These are the most common replacement parts that fix this problem. When you're ready to order, click below to find the right part at ProsourceParts.com — just search by your appliance model number for a guaranteed fit.
Helpful Repair Tip
To confirm a bad thermostat quickly, remove it and place it in a cup of ice water—if it does not show continuity when cold, replace it.
Frequently Asked Questions
How do I test the defrost thermostat on my FRT18G4AWC?
Unplug the refrigerator, remove the evaporator cover, pull the thermostat off the coil, and use a multimeter on continuity/ohms. Chill the thermostat in ice water—when cold it should show continuity (closed). Warm it and it should open. If it fails either state, replace it.
Can I replace the defrost thermostat myself and how long will it take?
Yes, a competent DIYer can replace it in 30–60 minutes. Turn off power, remove freezer items and the back panel, swap the thermostat (noting wiring and clip location), reassemble, and test. If you're uncomfortable with electrical work or removing panels, hire a technician.
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