What was found
ISOLATION VALVE DOES NOT OPEN WHEN SELECTED. APPEARS TO OPERATE CORRECTLY IN "AUTO"(BOTH PACKS IN AUTO, BOTH ENGINES AND APU BLEED ON, R DUCT PRESS &0 WITH ISOL OPEN. GROUNDED - YES. VERIFIED PILOT'S DISCREPANCY. VALVE DOESN'T OPEN INTERMITTENTLY, BUT WORKS IN AUTO & CLOSES CONSISTENTLY. SUSPECT ISOLATION VALVE STICKS INTERMITTENTLY. PERFORMED B737-900 FIM 36-10 TASK 806 INITAL EVAL. NO FAULT NOTED.