Short cycling after servicing traced to displaced thermistor sensor

What we found

We opened the indoor unit and checked the thermistor sensor position before testing any electronics.

• Thermistor sensor was hanging loose inside the unit — not clipped to the evaporator coil where it should sit
• Sensor reading showed room temperature instead of the lower coil surface temperature — confirming it was reading ambient air
• Control board was functioning correctly — it was responding to the sensor input as designed, just receiving the wrong data

During the general service, the technician knocked the thermistor sensor from its clip on the coil. The sensor began reading room air instead of coil temperature. The board got a falsely warm reading and shut the compressor down early. Each time the sensor read a rise, the compressor restarted. This created the short cycling pattern.

What we did

We re-seated the thermistor sensor into its original clip on the coil. The reading dropped to match the actual coil surface temperature. No parts were replaced.

The short cycling stopped as soon as the sensor was re-seated. The unit ran a full cooling cycle and held the set temperature without cutting off early. No control board repair or sensor replacement was needed.

What we learned

Short cycling after servicing — sensor position vs. sensor failure.

• The thermistor sensor clips onto the coil and reads its temperature. If it falls off during cleaning, it reads the warmer room air instead. The board then thinks the coil has reached target temperature too quickly. It shuts the compressor down early.
• Short cycling that starts right after servicing is almost always mechanical displacement, not electronic failure. The timing is the key clue.
• Re-seating the sensor in its clip is a no-parts fix. Testing the sensor reading against actual coil temperature confirms correct positioning.