What was found
" LEFT PACK OFF AMBER ALERT EICAS MESSAGE ON TAXI AC RETURNED TO BLOCK AND GROUNDED BY MAINTENANCE .DEFERRED LH PACK FOR DEPARTURE IAW ABX-MEL 21-51-1-1. AND RETURNED AC TO SERVICE WORKED A/C T/S PER W.D. 21-51-11 REACT. LH PACK FLOW CONTROL VALVE PER MEL MPM 21-51-2 PERFORMED OPS CK FOUND PACK WORKING NORMAL VALVE OPENING AND CLOSING GOOD AND INDICATION PACK OFF PERSIST. WITH PACK IN OPERATION DISCONNECTED CONN D2770 PACK OFF LIGHT EXTINGUISHED . REMOVED & REPLACED LH FCV PER AMM 21-51-01 OPS CK WITH APU GOOD. RAN ENGIBES CK GOOD NO INDICATION NOTED. THIS DI REMAIN OPEN AND DEACT. SYS PER MEL MPMP 21-51-2. A/C REMAIN NO ETOPS. 12/13/23 REFERENCE LP 38593-50/ 2+ 3 FOR FCU REMOVAL AND REPLACEMENT. PERFORMED OPS CHECK OF L/H PACK IAW B767 AMM 21-51-00. OPS CHECK GOOD AFTER MEL REACTIVATION PROCEDURE APPLIED. PLACARDS REMOVED. VERIFIED AIRCRAFT RELEASED TO ETOPS 180. PLACARD ROTATED. REF LP 38593-53/1"