What It Means
Open or shorted ambient outdoor air temperature sensor circuit.
Trane AC & Heat Pump
Trane AC & Heat Pump Error Code Red 5 Flashes
Troubleshooting guide for the Trane AC & Heat Pump system fault Red 5 Flashes.
Possible Causes
- Corroded, pinched, or loose sensor wiring connectors.
- Shorted ambient air temperature sensor.
- Open ambient air temperature sensor.
- Defective outdoor air sensor.
Not sure which one it is — or if it's none of these? Try ACLogics today.
Disclaimer: This information is for general reference. Error codes can vary by model and production year. Always refer to your machine's specific manual and the information printed on the unit itself.
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Full Diagnosis
Ambient (outdoor air) temperature sensor fault — the control board is reading an open or shorted circuit from the sensor that measures outdoor air temperature, which the board uses for defrost timing and low-ambient cooling lockout. This is a separate circuit from Red 6 Flashes (the outdoor coil temperature sensor, used for defrost sensing) and Red 13 Flashes (an external/auxiliary outdoor sensor on some installations) — all three sensors report similar-looking faults but fail independently of one another.
All Recorded Causes
Locate the ambient sensor (typically mounted at the outdoor unit's air inlet, separate from the coil sensor) and inspect its wiring and connector for corrosion, pinching, or looseness. If you can measure resistance, compare it against the temperature/resistance chart in the installation manual — a reading of zero (short) or infinite (open) confirms sensor failure. If the wiring and connector are intact but the fault persists, replace the ambient sensor; this is typically a low-cost part swap, not a control-board failure.
Verify Before Replacing Parts
- Confirm the exact Trane model family and ac and heat pump context before acting on a generic code description.
- Confirm filter condition, blower operation, and coil cleanliness before replacing any controls — start by ruling out whether locate the ambient sensor (typically mounted at the outdoor unit's air inlet, separate fro….
- Measure airflow-related readings that match the symptom, such as temperature split or static pressure, and check whether if you can measure resistance, compare it against the temperature/resistance chart in the….
- After the correction, run the system long enough to confirm the ac and heat pump fault does not return under normal load.
Not sure which system this Trane code is on?
ACLogics has guided diagnostics for 36 Trane fault codes and asks the right questions to narrow it down.
