Aircon Thermistor: What It Does, Common Issues, and What to Watch For
- thesnowflakesg
- May 8
- 2 min read
Summary
The thermistor is the temperature-sensing component inside your aircon system. It helps regulate cooling cycles by measuring room or coil temperatures. When it fails, the system may overcool, undercool, shut off too early — or not shut off at all. This article breaks down what the thermistor does, how it malfunctions, and what to look out for before bigger problems emerge.
What the Thermistor Does
Thermistors are heat-sensitive resistors that monitor either room temperature (ambient thermistor) or coil temperature (evaporator thermistor). The readings are fed to the PCB, which uses them to control the compressor, fan speed, and shut-off timing. Without accurate sensing, the aircon loses the ability to self-regulate — resulting in erratic performance or comfort issues.
What Damages the Thermistor
• Moisture or corrosion
Condensation buildup on the thermistor or coil may cause corrosion or shorting of the sensor leads.
• Component fatigue
Over time, especially in Singapore’s humid climate, the thermistor may drift from its original calibration — sending false readings.
• Disconnected or loose wiring
During repairs or cleaning, thermistor wires may get knocked loose or misconnected, leading to erratic behavior.
• Faulty placement
A mispositioned sensor may read airflow or casing temperature instead of true ambient or coil values — confusing the PCB.
⚠️ Thermistor faults often mimic gas issues, fan faults, or compressor failure. Only proper testing confirms the root cause.
Repair or Replace?
• Dirty or wet thermistor
This can be cleaned and reseated. In many cases, drying or repositioning restores normal function.
• Failed or out-of-spec thermistor
If readings are inconsistent or resistance values are off, the thermistor should be replaced. It’s a small, low-cost component — but crucial for stable operation.
A full system check is essential — poor cooling may not be a gas issue, but a faulty sensor.
How to Prevent Thermistor Issues
• Ensure proper drainage and airflow
Prevent coil condensation overflow or airflow restriction that can affect temperature readings.
• Don’t attempt DIY repositioning
Sensor alignment is precise. Shifting it by even a few cm can result in misreading and wrong shutoff cycles.
• Include sensor checks in servicing
Ask technicians to test thermistor resistance and placement as part of annual maintenance — especially in older systems.
What Happens If You Ignore It
✖ System may overcool or run too long
✖ Unit may short-cycle and fail to maintain room temperature
✖ Coil may ice over due to improper compressor control
✖ Comfort drops and energy usage rises — despite “no visible fault”
Final Word
The thermistor is small but critical. It quietly regulates the system’s ability to adapt to your room — and when it misreads, the entire cooling logic collapses. If your aircon behaves strangely but looks physically fine, the fault may lie in this sensor.
Cooling feels off but no obvious fault?