What was found
DURING CRUISE FROM PKWA, TAKEOFF PLUS 45 MINS TURNED ON RECIR FAN AND HEARD LOUD BANG FROM AREA UNDER CAPTAIN SEAT, COULD NOT STOP CABIN FROM CLIMBING. GOT CONTROL OF CABIN AT ABOUT 15,000, ACFT ALTITUDE CABIN WAS AT 10,2000. TURNED BLEED OFF ON LEFT SIDE, PRESSURE WOULD NOT GO DOWN. MANIFOLD PRESS AND TEMP STAYED AT 35 PSI AND 200C. MAINTENANCE TROUBLESHOT AND FOUND A LEAKING BLEED HEAT EXCHANGER ON NR 1 ENGINE PYLON. ALSO FOUND BAD PRESS REGULATOR ON NR 2 ENGINE. MAINTENANCE DEFERRED BOTH PER ALL APPLICABLE MANUALS. AIRCRAFT WAS RETURNED TO SERVICE.