What was found
LEFT ENGINE BLEED OFF LIGHT ILLUMINATED WITH LT ENG BLEED OFF EICAS MESSAGE WITH ENG RUNNING, BLEED SWITCH ON & ISOLATION VALVE CLOSED. PACK ON WITH DUCT PRESSURE ZERO. BLEED LIGHT STAYS ON WITH THROTTLES ADVANCED ABOVE 41 PERCENT N1. RECORD DUCT PRESSURE WHEN ADVANCED. LT ENGINE BLEED OFF EICAS. FOLLOWED PROCEDURE, LIGHT OUT MOMENTARY THEN BACK ON. PRESS ZERO. DEFERRED BLEED INOP, CLOSED. REPLACED FAN AIR TEMP SENSOR. RAN NR 1 ENGINE DUCT PRESSURE 20 PSI AT IDLE. BLEED LIGHT OPERATES NORMALLY.