# SDR ASAA2021112036673

- Type: Service difficulty report (as reported; unverified)
- Difficulty date: November 20, 2021
- Submitted: November 24, 2021
- Operation: Air carrier
- Aircraft: [N471AS](https://openairdocs.org/aircraft/N471AS), registered now
- Make and model: Boeing 737990ER
- Aircraft serial: 41703
- Aircraft time: 26,724 hours, 8,489 cycles
- System (JASC): [2160 · Cabin Temperature Control System](https://openairdocs.org/jasc/2160)
- Part: Modulating Valve
- Part number: 3989085
- Part serial: 7737
- Condition: Failed
- Location: Left Ecs Bay
- Part time: 60,019 hours, 19,392 cycles
- Stage of operation: DE
- How discovered: V
- Nature of condition: J
- Precautionary procedure: O
- FAA source: FAA Service Difficulty Reporting System (https://sdrs.faa.gov/)
- Page: https://openairdocs.org/sdr/ASAA2021112036673

## Discrepancy

LEFT PACK LIGHT ILLUMINATED ON DESCENT LIGHT EXTINGUISHED W MASTER CAUTION RESET. GROUNDED - YES. PERFORMED BITE CHECK ON #1 ZONE TEMP CONT, CONFIRMED HARD FAULT ON TCV. REPLACED LH PACK TCV PER B737-900 AMM 21-51-10, GREEN "GO" LIGHT ILLUMINATED.

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