Frigidaire FRT18G4AWC Thermostat Replacement – How to Diagnose & Replace
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Understanding the Problem
This guide covers the two different thermostats you may mean on a Frigidaire FRT18G4AWC: the user temperature-control thermostat (the control that calls the compressor to run) and the defrost thermostat (mounted to the evaporator coil that protects the defrost heater and controls defrost cycles). Both can cause cooling problems, but they behave differently. Read the steps below to identify which thermostat is faulty and follow the replacement instructions. 1) Identify which thermostat is the issue - Symptom check: If the whole refrigerator is warm and the compressor never runs, start with the temperature-control thermostat (the user control). If you have frost/ice buildup on the evaporator and the freezer is cold only when you manually defrost, suspect the defrost thermostat (or a related defrost component). - Visual inspection: Remove the control knob and look behind the control housing for a mechanical thermostat. The defrost thermostat is clipped to the evaporator coil inside the freezer compartment behind the evaporator cover. 2) Tools and prep - Tools: multimeter, nut drivers (1/4" and 5/16"), Phillips screwdriver, flat screwdriver, needle-nose pliers, work gloves, small container for screws, flashlight. - Prep: Unplug the refrigerator or turn off breaker. Remove food from the freezer if you need to open the evaporator area. Allow easy access and work on a dry surface. 3) Testing the temperature-control thermostat (user control) - Access: Pull off the control knob, remove the control housing screws and slide the thermostat assembly out so you can access the wiring and switch. - Visual test: Inspect for burned terminals, melted plastic or loose wires. - Continuity test: Set your multimeter to Ohms. With the thermostat in the OFF position you should have an open circuit. Rotate the dial to a mid-cool setting — you should see continuity between common and the compressor output terminal when the thermostat calls for cooling. Rotate through several positions to see the switch open/close. No change or no continuity at any setting → thermostat likely bad. - Live test (optional, only if comfortable and safe): With power on and meter set to AC volts, measure voltage to compressor relay when thermostat is set to call for cooling. If voltage never appears but the thermostat shows no continuity, replace the thermostat. 4) Replacing the temperature-control thermostat (mechanical) - Unplug the refrigerator. Remove the control knob and housing screws. Note wiring positions or take a picture for reassembly. - Disconnect the wiring harness or carefully pull off the spade terminals (use needle-nose pliers). Remove the retaining clip or screws holding the thermostat and withdraw it from the cabinet. - Install the new thermostat in the same orientation. Reattach wires to the same terminals, re-seat the housing and knob. Restore power and test by turning the dial to a cold setting — the compressor should engage within a few minutes. 5) Testing the defrost thermostat (thermostat clipped to evaporator) - Access: Unplug refrigerator. Remove freezer shelves, ice maker (if required), and the evaporator access cover inside the freezer. You may need to remove the back panel inside the freezer. - Visual: Inspect the defrost thermostat clip and wiring; look for heavy frost or ice accumulation and for a thermostat physically broken or corroded. - Cold continuity test: Remove the defrost thermostat from the coil (disconnect its wires). At room temp many defrost thermostats are open; when cooled to near 32°F (0–5°C) they close. Use a multimeter to check continuity. To test operation quickly, place the thermostat in a cup of ice water (be sure the electrical terminals stay dry) and watch for continuity to appear. If it never closes when cold, it is faulty. - System-level check: If the defrost thermostat is good but you still have frost build-up, check the defrost heater and the defrost control (timer or electronic control board) for continuity and for proper operation. 6) Replacing the defrost thermostat - Unplug refrigerator. Remove freezer back cover to expose the evaporator and defrost components. - Note how the thermostat is clipped to the evaporator coil and how the wiring is routed. Disconnect the two-wire connector or remove spade connectors. Remove the clip or foam mounting and take out the old thermostat. - Install the new thermostat in the same location (clipped firmly to the evaporator coil or in the same thermal contact). Reconnect wires and reseal any foam or insulation you removed. - Reassemble the back cover, restore power and run a manual defrost test if your model has a diagnostic or timer: force a defrost cycle (by following the service manual procedure or by advancing the mechanical timer) and confirm the defrost heater runs and that the defrost thermostat opens/closes appropriately. 7) Final checks and common follow-ups - After replacement, monitor for 24–48 hours. Verify the compressor cycles, the freezer and fresh-food temps stabilize, and there is no abnormal frost accumulation. - If cooling still fails after a good temperature-control thermostat, check start relay/capacitor and compressor. If frost returns despite a good defrost thermostat, test the defrost heater element and defrost control/timer/board. Safety note: Always unplug the appliance before doing electrical work. If you are not comfortable testing live circuits, hire a technician. Replacing components on the evaporator requires care to avoid puncturing the refrigerant lines — do not drill or force parts around the evaporator coil.
Common Symptoms
Entire refrigerator not cooling (compressor doesn’t run) or freezer frost buildup and no automatic defrost. Intermittent cooling cycles or thermostat knob that doesn’t click or change compressor state.
Common Causes
- Faulty user temperature-control thermostat (mechanical switch not closing)
- Defrost thermostat failed (won’t close at low temp or not opening in defrost)
- Related component failure (defrost heater or defrost control board, start relay, compressor) causing similar symptoms
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Helpful Repair Tip
Use a multimeter continuity test and a simple ice-water test for the defrost thermostat: the defrost thermostat should close (show continuity) when chilled in ice water. For the control thermostat, check for continuity only when the dial is set to call for cooling.
Frequently Asked Questions
How can I tell whether I need the defrost thermostat or the main temperature-control thermostat?
If the compressor never runs and the fridge is warm, start with the main temperature-control thermostat (the control behind the knob). If you have heavy frost on the evaporator and the freezer slowly gets warmer between manual defrostes, the defrost thermostat (or defrost heater/control) is more likely. Use the continuity tests: the user thermostat should show continuity when set to call for cooling; the defrost thermostat should close when chilled in ice water.
Can I replace these thermostats myself and how long will it take?
Yes — if you are comfortable with basic electrical testing and simple disassembly. Replacing the user temperature-control thermostat typically takes 20–45 minutes. Replacing the defrost thermostat (inside the freezer behind the evaporator cover) takes 30–90 minutes depending on how much disassembly is required. Always unplug the fridge first and document wiring locations or take photos before disconnecting anything. If unsure, call a qualified appliance technician.
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