What was found
AIR TURNBACK DUE TO LEAVING TEN THOUSAND FEET (10,000') CABIN CLIMBED AT 1000' FT/MIN TO 9800' CABIN. MAIN OUTFLOW CLOSED MANUAL A/C NO HELP. AIRCRAFT MADE AN UNVENTFUL LANDING TO TPA. RESECURE CHECK VALVE EXTERNAL AIR CONDITION CONNECTION. PRESSURIZATION A/C AND OPS CK NORMAL PER BOEING MM. C/W CABIN PRESSURIZATION INSP PER BOEING MM. NO DEFECTS NOTED. (LP36781)