Auto mode kept shutting off: sensor thought the room was already cold
The aircon ran fine in cool mode but kept cycling off in auto, so the owner stopped using auto altogether. The symptom pointed to one suspect: something was telling the system the room was colder than it really was.
By Team Snowflake | Reviewed 14 Mar 2026
Case summary
Daikin Wall-mounted7 years oldHDBJurong East, Singapore
- Concern
- The owner assumed the auto mode feature itself was faulty and had switched to manual mode to avoid it.
- Found
- room temperature sensor circuit on control board was reading erratic temperatures, causing auto mode logic to shut down thinking room was cold enough
- Key check
- Compared actual room temperature against the temperature readings displayed on the control panel. They did not match
- Result
- Auto mode held a steady cycle with no more unexpected shutdowns, and the owner went back to using it daily.
What we were told
In auto mode, the aircon shut off and restarted on its own every few minutes. Cool mode ran without trouble, so the owner had given up on auto. The pattern had been getting worse over several weeks.
What we checked
Auto mode reads the room temperature sensor to decide when to ramp down or shut off the compressor. If that reading drifts, the unit acts on a room temperature that does not exist. We compared what the panel thought the room temperature was against a separate thermometer held at the same height, so both readings reflected the same air. A steady, accurate sensor would track the thermometer closely. The size of the gap, and whether it held steady, would tell us whether the sensor or the control board was at fault.
The separate thermometer showed the room was still warm.
The unit display read the room as much colder than it really was.
The sensor output was unstable, jumping between cold and warm readings within seconds.
The outdoor temperature sensor read steady and within its expected range.
What we found
The indoor temperature sensor had degraded inside. Its reading drifted instead of tracking the room steadily. When it read too cold, auto mode decided the room had reached the set point and shut the compressor off. Seconds later the reading shifted again, so cooling restarted. The outdoor sensor and control board both worked correctly, which isolated the fault to the indoor temperature sensor alone.
What fixed it
We replaced the degraded ambient temperature sensor with the correctly rated part for this Daikin model. After fitting it, we checked that the panel display matched the separate thermometer within one degree at several room positions. We then ran the unit through a full auto-mode cycle at the owner's usual set temperature. The compressor ramped down smoothly once the room reached the target, held steady without cycling, and restarted only when the room naturally warmed up. No control board replacement or software reset was needed.
Outcome
Auto mode held a steady cycle with no more unexpected shutdowns, and the owner went back to using it daily.
What this case teaches us
Auto mode is only as good as the temperature it reads
- Auto mode decides when to stop cooling based on the room temperature sensor. A drifting sensor makes the unit shut off too early, even when the room is still warm.
- When auto behaves oddly but cool mode is fine, the sensor is a far more likely cause than the control board or compressor.
- Check the temperature on the panel against a separate thermometer. A gap between the two points straight at the sensor, and a sensor swap is a far smaller job than a board.
Related reading
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