What was found
UNABLE TO CONTROL PRESSURIZATION WITH ANY MODE (AUTO, STANDBY, OR MANUAL). DESCENDED TO 11,000. PERFOMED OPS CHECK OF CABIN PRESS CONTROL SYSTEM PER MM 21-31-000-1 ALL MODES OP CHECK NORMAL. VERIFIED CABIN OUTFLOW VALVE IS CLOSED WHEN COMMANDED CLOSED. WITH APU ATTEMPTED TO PRESSURIZE A/C TO PERFORM DECAY CHECK APU WOULD ONLY BRING A/C TO 3.1DP., WHILE USING EXTERNAL AIR SOURCE THE HUFFER OVERHEATED. ALSO WHILE A/C WAS PRESSURIZED. FOUND AIR STILL COMING FROM THE AVI EXHAUST EVEN THOUGH THE VALVE WAS WRENCHED CLOSED. REPLACED EQUIP COOLING FLOW CONTROL VALVE REF M.M 21-58-021-4. PERFORMED DECAY CK REF MM 05-51-101-2, GROUND OPS CK GOOD AT THIS TIME. ACFT OK FOR SERVICE.