How do I fix error code F-DEF-SENSOR on a Samsung refrigerators?

1. undefined: Check CN20 connector seating 2. undefined: Measure voltage between CN20 pin 6 (BLU) and pin 8 (W/GRY) — expect 0.6V to 4.6V 3. undefined: Disconnect and measure resistance at CN20-6 to CN20-8; expected 13.29 kΩ at 32°F (0°C) 4. undefined: 0 Ω = shorted sensor; ∞ Ω = open sensor or broken wire — replace sensor 5. undefined: If resistance is normal, inspect PCB solder at R223

Samsung Refrigerators2020–present

Error Code F-DEF-SENSOR

Defrost sensor on freezer evaporator is failed or disconnected

Moderate

Address soon - your appliance may not work properly

Also displayed as: F blinks (defrost sensor indicator)

What This Means

Failed defrost thermistor (502AT) — open or short circuit; Loose or disconnected CN20 connector; Damaged harness wiring; Bad solder at R223 on Main PCB (IC01 MICOM pin 6)

What actually causes this:

The sensor that tells the board when the evaporator is warm enough to end a defrost cycle is bad — the unit may over-defrost or under-defrost.

First Thing to Check

Inspect the defrost sensor clip on the freezer evaporator fins — it may have fallen off or been knocked loose.

Parts Involved

F-DEF thermistor (502AT)Main PCBCN20 connector

How to Fix

1
Check CN20 connector seating
2
Measure voltage between CN20 pin 6 (BLU) and pin 8 (W/GRY) — expect 0.6V to 4.6V
3
Disconnect and measure resistance at CN20-6 to CN20-8; expected 13.29 kΩ at 32°F (0°C)
4
0 Ω = shorted sensor; ∞ Ω = open sensor or broken wire — replace sensor
5
If resistance is normal, inspect PCB solder at R223

This Error Applies To

Samsung RF28T5 Series Refrigerators (2020) (2020–present)

Service manual exact match: RF28T5101SR/AAService manual exact match: RF28T5A01S9/APService manual exact match: RF28T5021S9/EMService manual exact match: RF28T5001S9/MLService manual exact match: RF28T5021B1/COService manual exact match: RF28T5A01SR/AAService manual exact match: RF28T5021SR/AAService manual exact match: RF28T5001SR/AA