What was found
APU VALVE DISAGREE LIGHT DISPLAYED. VALVE CLOSED NORMALLY AND CB PULLED AND COLLARED. APU BLEED WOULD NOT OPEN AFTER STARTING LT ENG. AFTER ACFT RETURNED TO GATE AND LT ENG SHUTDOWN, APU BLEED VALVE OPERATED NORMAL. CHECK APU SHUTOFF VALVE INTERLOCK CIRCUITRY. OTHER POSSIBLE CAUSE: APU BLEED CHECK VALVE. OPS CHECK THIS ITEM WHILE STARTING BOTH ENGS BEFORE CLEARING THIS DF ITEM. FOUND LT ENGINE INDICATION INTERMITTENT AT BLEED SWITCH AND UPPER EICAS ADVISORY MESSAGE, REPLACED THE LT BLEED AIR CONTROL CARD, OPS NORMAL.