What was found
DEPARTED & EN ROUTE, APPROX 15 - 20 MINS AFTER LEVELING OFF AT FL 360 THE CABIN ALTITUDE WARNING ILLUMINATED. DECLARED AN EMER & INITIATED AN EMER DESCENT & DIVERTED. THE CABIN ALT. STAYED BELOW THE POINT OF O2 MASK ACTIVATION & ONCE THEY DESCENDED TO A SAFE ALTITUDE THEY OPERATED THE PRESSURIZATION IN MANUAL MODE WITH NORMAL OPERATION. THE PRESSURIZATION AUTO MODE WAS MEL'D & THE ACFT REPOSITIONED FOR TROUBLESHOOTING. WILL AMEND REPORT WITH FINDINGS.