New board didn't fix it: the temperature sensor was at fault

The unit cooled for two or three hours, then went quiet. No error code, no warning light. The control board had already been replaced and the shutdowns carried on exactly as before, which usually means the wrong part was blamed.

By Team Snowflake | Updated 28 Jul 2026

Case summary

Mitsubishi Electric Wall-mounted7 years oldCondoBukit Panjang, Singapore

Concern: The homeowner had already paid for a control board replacement that did not fix the shutdowns. The next suggested step was a compressor check, which would have meant another large bill.
Found: Room temperature sensor had drifted, sending a lower-than-actual reading to the control board. The unit thought the room was already cold and shut off early.
Key check: Compared the sensor reading with the real room temperature. It was low enough to make the unit shut off early.
Result: The unit ran through a full afternoon without cutting out. Both the new control board and the original one it replaced had been working correctly the whole time. A drifted sensor, one of the cheapest parts in the unit, had been driving every shutdown.

What we were told

The bedroom unit runs for two or three hours, then goes quiet. No blinking lights, no error code. The control board had already been replaced, but the shutdowns continued. The compressor was the next thing feared, which worried the homeowner since the board change had settled nothing.

What we checked

A clean shutdown with no error code usually means the board thinks the room has reached the set temperature and switched off on purpose. The board only acts on what its sensors tell it. So instead of testing the new board or the compressor, we checked what the board was actually reading. We ran the unit through a full cooling cycle and compared the sensor reading against the real room temperature with our own thermometer.

The compressor ran steadily for the first hour with consistent cooling output.
After about ninety minutes, the compressor stopped while the room was still clearly warmer than the set temperature.
The room sensor reported a temperature lower than the room actually was, low enough to make the unit shut off early.
Power, wiring, and the new board itself all checked out as healthy.

What we found

The room temperature sensor had drifted with age and was reading low. It told the control board the room had reached the set temperature while the room was still warm. The board did its job correctly and shut the compressor down on that false reading. The earlier board swap changed nothing because the new board was wired to the same old sensor and received the same wrong number. The compressor was never the problem.

What fixed it

We fitted a matched replacement room temperature sensor for this Mitsubishi Electric unit. With an accurate reading reaching the board, the compressor stayed on until the room genuinely reached the set temperature, then cycled normally. No control board or compressor work was needed, so the homeowner avoided the larger bill they had been quoted.

Outcome

The unit ran through a full afternoon without cutting out. Both the new control board and the original one it replaced had been working correctly the whole time. A drifted sensor, one of the cheapest parts in the unit, had been driving every shutdown.

What this case teaches us

A new board that does not fix it points to the sensor

When a unit shuts off cleanly with no error code, the board is following a sensor reading. Check the sensor before blaming the board or the compressor.
A replacement part that changes nothing is a strong clue the original part was healthy. The fault sits elsewhere in the chain.
A drifted temperature sensor is cheap to replace and easy to miss. It can mimic a far more expensive board or compressor fault.

Questions this case answers

Aircon shuts off every few hours with no error code: what is wrong?

A clean shutdown with no code usually means the board believes the room has reached set temperature and has switched off on purpose. It acts only on what its sensors report. In this Bukit Panjang condo the room sensor read lower than the room really was, low enough to stop the compressor while the room stayed warm.

A new control board did not fix it. What does that tell you?

That the original one was probably healthy and the fault sits elsewhere along the chain. The replacement was wired to the same old sensor and received the same wrong number, so nothing changed. Power, wiring and the new board all tested healthy while the shutdowns carried on exactly as before.

What is sensor drift and how would anyone spot it?

A temperature sensor can lose accuracy with age and start reporting a figure that no longer matches the room. Spotting it means comparing its reading against a real thermometer through a full cooling cycle. The compressor here ran steadily for an hour, then stopped at around ninety minutes with the room still clearly warm.

Is the compressor next if a board swap did not work?

Not on the evidence from this unit. One of the cheapest parts inside it was driving every shutdown. A matched replacement room sensor for this Mitsubishi Electric model was fitted, and with an accurate reading reaching the board the compressor held on until the room genuinely reached set temperature, then cycled normally.

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