Air Conditioner
Samsung
Updated Jul 28, 2026
Samsung AC E121 Error — Room Temperature Sensor Fault & Fix
E121
Samsung · Air ConditionerE121 on a Samsung AC means the indoor room temperature sensor (thermistor) has an open or…
Quick answer
E121 on a Samsung AC means the indoor room temperature sensor (thermistor) has an open or short circuit.
What E121 means
The room temperature sensor measures the ambient air returning to the indoor unit. When this sensor fails (open or shorted), the PCB cannot regulate the compressor speed or decide when to cycle off — so it displays E121 and stops.
How to fix it
The sensor is usually a small thermistor near the air-return grille. It is inexpensive and easy to replace.
What does the E121 code mean?
E121 indicates the indoor room temperature thermistor is open-circuit or short-circuit. The unit cannot measure room temperature.
Common causes
- Faulty room thermistor (resistance out of range)
- Loose connector on the indoor PCB
- Damaged wiring between sensor and board
- Indoor PCB fault (rare)
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How to fix the E121 error
Power off
Switch the breaker off.
Locate the sensor
Open the indoor unit front panel. The room sensor is typically clipped near the return-air grille, with a two-wire lead running to the main PCB.
Check the connector
Unplug and reseat. Inspect for corrosion.
Measure resistance
At 25°C a standard Samsung thermistor reads around 10 kΩ. Open-line or zero means replace.
Replace if needed
Swap the thermistor and plug in the new one.
Safety first: Always isolate power before opening the indoor unit.
Part you may need: Room temperature thermistor (10 kΩ NTC)
Quote the full model number when ordering — different Samsung series use slightly different thermistor values.
Frequently asked questions
Is E121 serious?
Not dangerous, but the AC will not run until the sensor is replaced or reconnected.
Can a dirty filter cause E121?
No. E121 is an electrical sensor fault, not an airflow issue — though a clogged filter can cause other problems.
✎ Written by
REZAUL Karim (Riad)
REZAUL Karim (Riad) is the founder of ErrFixHub and a hands-on electronics and home-appliance repair specialist with over 15 years of experience diagnosing and fixing air conditioners, washing machines, refrigerators, inverters and other household appliances. He built ErrFixHub to turn cryptic error codes into clear, step-by-step fixes anyone can follow — cross-checking every code against manufacturer documentation and real repair-bench experience.
