Aircon Outdoor Thermistor
The outdoor thermistor monitors temperature near the outdoor unit and compressor. When it drifts or fails, it can trigger a false overheat shutdown. This looks exactly like a real heat problem — but the cause is different.
What This Part Does
The outdoor thermistor reads temperature near the outdoor unit components and the discharge line. The outdoor PCB uses this data to make protection decisions.
If the sensor reads too high — real or false — the board shuts down the compressor to prevent damage.
A working sensor protects the system during genuine heat stress. A drifting sensor triggers that same protection when there is no real risk.
How You Would Notice
The aircon runs normally, then stops. On cooler days it runs without issue. On hot afternoons it trips.
After it stops, it often resumes after a short wait. The pattern is heat-related and time-dependent.
You may notice it gets worse over weeks or months. The threshold for stopping seems to get lower.
- Aircon stops during hot periods but works fine in cooler conditions
- Unit resumes after a short rest but stops again in heat
- Pattern worsens gradually over time
It Might Not Be The Sensor
Real heat problems cause the same pattern. A dirty outdoor coil or a blocked outdoor unit cannot reject heat fast enough. The system overheats. Protection shuts it down — correctly.
Replacing the sensor when the real problem is a dirty coil or blocked outdoor unit does nothing.
We confirm heat rejection is adequate before we look at the sensor.
How We Check
We start with heat rejection. We check the outdoor coil condition and airflow path. If the coil is dirty or airflow is blocked, we address that first and retest.
If heat rejection is normal, we compare the sensor reading against actual measured outdoor temperature. A working sensor should track closely.
A meaningful gap between sensor reading and measured temperature confirms sensor drift.
We only recommend sensor replacement when both checks support sensor error.
What We Find And What Happens Next
We replace the sensor only when heat rejection is confirmed adequate and the sensor reading is proven wrong.
| Finding | Next Step |
|---|---|
| Outdoor coil dirty or airflow blocked | Clean coil or clear path, retest |
| Heat rejection normal, sensor mismatch confirmed | Replace outdoor thermistor, retest |
About The Repair
Outdoor thermistor replacement is a minor repair. The sensor is a small part and the job is straightforward once the fault is confirmed.
If a technician recommends sensor replacement without checking coil condition and airflow first, ask what was measured.
A confirmed sensor fault has a temperature mismatch reading. If there is no measurement, the fault has not been confirmed.
After Replacement
A replaced outdoor sensor should restore normal operation in hot weather. The unit should run through hot afternoons without false shutdowns.
If shutdown continues after sensor replacement, the coil condition or heat rejection path needs to be re-examined.
We confirm operation under hot-load conditions before closing the job.
When We Tell You To Wait
If the unit only trips on the very hottest days and resumes quickly, it may be marginal heat rejection rather than sensor failure.
A coil clean is often worth doing before diagnosing the sensor — it may resolve the issue entirely.
We will tell you on-site what the data shows.