What was found
AIR TURNBACK, AIRCRAFT WOULD NOT PRESSURIZE, OUTFLOW VALVE INDICATED CLOSED. ATTEMPTED TO ISOLATE MALFUNCTION NO HELP. ON DESCENT A/C WOULD ALTERNATELY PRESSURIZE AND DEPRESSURIZE. REPLACED EQUIPMENT COOLING FLOW CONTROL VALVE, PRESSURIZED AIRCRAFT. VALVE FUNCTIONS NORMALLY. TT 0060115 M+E =03-2158-9-0001. HISTORY: A/C EXPERIENCED CABIN PRESSURE PROBLEM ON 8 MAY RESULTED IN REPLACEMENT OF RT PACK FLOW VALVE M+E 03-2152-9-0001 S/N 1969. RECOMMENDATION: REMAIN OPEN PENDING REVIEW OF TEARDOWN REPORT.