American Standard AC & Heat Pump Error Code Red 15 Flashes

Full Diagnosis

Duplicate outdoor temp sensor detected — the control board is receiving two conflicting outdoor-ambient temperature signals instead of one and can't determine which reading is valid. This differs from Red 5 (a single ambient sensor reporting open/shorted) or Red 13 (a fault on a separate external outdoor sensor); Red 15 specifically means the board sees redundant wiring or a duplicate sensor on the same input rather than a failed one. Left unresolved, it can affect defrost and low-ambient cooling lockout decisions since the board isn't sure which temperature to trust.

All Recorded Causes

Remove or disconnect any redundant outdoor sensor if two are installed — this can happen after a service call where a replacement sensor was added without removing the old one, or from a wiring harness mistake. If only one sensor exists, try resetting power; if the code persists with a single sensor confirmed present, the fault likely lies in the control board's sensing circuit and continued errors may require technician support.

Verify Before Replacing Parts

1. Confirm the exact American Standard model family and ac and heat pump context before acting on a generic code description.
2. Verify the sensor or thermistor reading against the expected range for the current operating condition, keeping in mind that remove or disconnect any redundant outdoor sensor if two are installed — this can happen a….
3. Check the sensor harness and board connection before condemning the sensor itself; on American Standard units this is also where you'd confirm if only one sensor exists, try resetting power; if the code persists with a single sensor….
4. After the correction, run the system long enough to confirm the ac and heat pump fault does not return under normal load.