Short cycling after service: sensor knocked out of its clip

The unit cooled fine before the service visit, then began cutting off every few minutes and restarting on its own. The servicing company returned and said the temperature sensor had failed and needed replacing. The timing pointed somewhere else.

By Team Snowflake | Updated 28 Jul 2026

Case summary

Midea Wall-mounted4 years oldHDBPaya Lebar, Singapore

Concern: The homeowner feared the service work had damaged the control board, meaning a costly electronic repair.
Found: temperature sensor was displaced from its clip during servicing, reading room air instead of coil temperature
Key check: Checked sensor position and reading against coil surface temperature to confirm displacement
Result: The short cycling stopped at once. The unit completed a full cooling cycle and held its set temperature without cutting off early.

What we were told

The aircon was working fine until a general service was carried out. Afterwards it started turning off after a few minutes, then restarting. It keeps cycling on and off. A failed temperature sensor seemed the obvious answer, with a replacement the suggested fix.

What we checked

Because the fault started right after the service, we checked the sensor position before testing any electronics. We removed the front cover and filter panel to reach the coil. Then we looked at whether the temperature sensor still sat in its clip on the coil surface. We also compared its reading against a contact thermometer on the coil, to see what the board was being told versus the real coil temperature.

The temperature sensor hung loose inside the unit, no longer clipped to the coil.
Its reading matched room temperature, not the cooler coil surface it should track.
The control board responded correctly to that reading. It worked as designed, but on wrong data.

What we found

During the earlier service, the temperature sensor was knocked out of its clip on the coil. The clip is small and the probe sits in a narrow channel along the coil surface, so a cleaning brush or a refitted filter panel can dislodge it. Once loose, the probe hung in the airstream and read room air instead of the coil. That reading ran several degrees warmer than the coil itself. The board took it to mean the coil had reached set temperature and stopped the compressor. With the compressor off, the air warmed a little, the reading rose further, and the board restarted. That loop produced the rapid on-off pattern the homeowner described.

What fixed it

We pushed the temperature sensor back into its clip on the coil surface. The clip was intact, so the probe only needed reseating. We then confirmed the sensor reading matched the contact thermometer on the coil within one degree. With the unit reassembled, we ran a complete cooling cycle and watched the compressor stay on without cutting out until set temperature was reached. No parts were replaced, and no electronic testing was needed beyond checking the reading.

Outcome

The short cycling stopped at once. The unit completed a full cooling cycle and held its set temperature without cutting off early.

What this case teaches us

A fault that appears right after a service usually traces to the work

The unit cooled fine before the visit and failed straight after. That timing points to the work done, not a worn-out part.
A sensor knocked out of its clip reads room air, not coil temperature, so the board cuts the compressor early and the unit short cycles.
Tell the next technician the service date and what was done. It separates a workmanship slip from a genuine new fault.

Questions this case answers

Aircon cutting off every few minutes after a service visit: what changed?

Something the visit disturbed. In this Paya Lebar flat the temperature sensor hung loose inside the unit, no longer clipped to the coil. Its reading matched room air rather than the cooler coil surface it should track, so the board stopped the compressor early, then restarted it moments later, over and over.

What is short cycling and how does a loose sensor cause it?

Short cycling means the unit switching on and off in rapid bursts instead of running to set temperature. The probe hanging in the airstream read several degrees warmer than the coil. The board took that as coil temperature reached and cut the compressor. Air then warmed a little more, the reading rose, and it restarted.

How does a sensor get knocked out during cleaning?

The clip is small and the probe sits in a narrow channel along the coil surface. A cleaning brush or a refitted filter panel can dislodge it without anyone noticing. The clip on this unit was still intact, so the probe only needed pushing back into place, with no part replaced and no electronics tested.

Should I mention the service date to the next technician?

Yes, along with what was done. That timing is diagnostic on its own and separates a workmanship slip from a genuine new fault. Here it sent the check to the sensor position before any electronics were touched, and the reading was then verified against a contact thermometer on the coil within one degree.

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