What was found
CAPTAIN REPORTED LEFT ENGINE WITH N2 47 PERCENT IN IDLE POSITION. DURING MAINTENANCE REVISION WAS DETECTED LEFT ENGINE WITH N2 52 PERCENT, EPR 1.03; ENGINE STABILIZED AT N2 50 PERCENT, EPR 1.03. WHEN LEFT AIR CONDITIONING SWITCH WAS OPERATED N2 48 PERCENT, EPR 1.02 AND WITH ELECTRICAL CHARGES N2 TREND TO LET OUT OF SERVICE LEFT GENERATOR. ENGINES WERE SHUTDOWN AND AIRCRAFT WAS SENT TO THE HANGAR, FCU WAS REPLACED IAW MM 73-20-01, TRIMMING AND ADJUSTMENT WERE PERFORMED IAW MM 71-00-00, TESTED CORRECT.