Indoor Room Temperature Sensor Error
What it means
This code appears on Samsung inverter split wall units such as WindFree and Digital Inverter. It means the room temperature thermistor in the indoor unit is open or shorted, so the indoor board cannot tell the room temperature. The unit usually stops cooling until the sensor is fixed. The same code can mean something else on other brands.
Models covered: Samsung inverter split air conditioners (e.g. WindFree and Digital Inverter wall units) that show three-digit E codes on the display.
Symptoms3
- E121 shows on the indoor unit display.
- Cooling does not start, or stops after a short run.
- The fault may appear after cleaning the filters or removing the front cover.
Possible causes5
- Sensor plug not fully seated on the indoor board after service or from vibration.
- Sensor failed with age.
- Sensor wire cut or pinched under the cover.
- Moisture or corrosion on the connector.
- Faulty sensor input on the indoor PCB.
How to diagnose5
- Switch off the breaker for a few minutes, then restart.
- With the power off, open the front cover and check the sensor is in its clip and its wire is not pinched.
- A technician measures the sensor resistance against the resistance-temperature table in the Samsung service manual.
- Inspect the plug and socket on the indoor board.
- If the sensor is good, the indoor PCB is the suspect.
How to fix5
- Reseat the plug and put the sensor back in place.
- Repair a cut wire.
- Replace the room temperature sensor.
- Replace the indoor PCB if the sensor is proven good.
- Run the unit and confirm normal cooling without the code returning.
Repair cost
In Saudi riyals; the highlighted part is the expected range for this fault.
In the Saudi market: SAR 80–1,200 (≈ USD 21–320)
Our prices come from the Saudi market, converted at a fixed rate (SAR 3.75 per USD). Prices in your country may differ a lot, so we show the cost level.
It is usually a cheap sensor plus labor; the top of the range covers a new indoor PCB.
Prices are rough estimates including the part and the technician’s fee, and vary with brand, model and part source.
Prices last updated: September 2026
Frequently asked questions
E121 appeared after cleaning the filters. Is that normal?
The sensor may have slipped out of its clip or its wire got pinched when the cover went back on. Switch off and check it; if the code stays, it needs testing.
Can I use the AC until the technician arrives?
Usually the unit will not cool with this code. One restart attempt does no harm, but repeating it will not help.
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