As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT FL280 ABOUT TO DESCEND INTO ICING WE TURNED ON WING ANTI-ICE. RECEIVED LVL 1 AIR SYS 3 OFF WITH RED MANIFOLD NR 3 INDICATION BOTH ON SCHEMATIC AND AIR SYSTEM CONTROL PANEL BLEED AIR 3 MANIFOLD LIGHT. CONSULTED WITH MOCC DIVERTED TO AVOID KNOWN ICING. REMOVED AND REPLACED NR 3 MANIFOLD FAILURE DETECTION PRESSURE SWITCH PER AMM 36-23-03-4-0.