What was found
CAPTAIN REPORTED THAT WHEN LEFT THRUST LEVER WAS LOCATED IN IDLE POSITION THE AIR-CONDITIONING PACK WAS SHUTDOWN AND "HI STAGE" LIGHT TURNED ON. DUAL VALVE WAS REPLACED IAW MM 36-11-08, ALL CORRECT. DURING ENGINE STARTING, "HI STAGE" LIGHT DID NOT TURNED OFF, ENGINES WERE SHUTDOWN AND PILOT REGULATOR WAS RESEATED, LIGHT TURNED OFF. LEFT ENGINE WAS STARTED AND FAIL CONTINUE. AIRCRAFT WAS SENT TO THE HANGAR, LEFT HIGH PRESSURE SHUTOFF VALVE WAS REPLACED IAW MM 36-11-07, TESTED CORRECT.