As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF WHEN LP BLEEDS WERE PLACED IN AUTO A STRONG METALLIC OR POWDERY ODOR WAS EMITED FROM DUCTS AND ODOR WAS STRONGER IN THE COCKPIT. ODOR PERSISTED AND ONLY DECREASED BY SHUTING OFF THE RECIRCULATION FAN. RETURNED TO DTW. MAINTENANCE GROUND RAN AC WITH LP AND HP BLEEDS ON AT VARIOUS TEMP SETTINGS. NO ODOR NOTED. ALL CHECKS GOOD.