What was found
CLIMBING THRU 10,000 FEET, ALT WARNING HORN WENT OFF AND CABIN ALT 10,000 FEET. WENT TO MANUAL AND SWITCHED TO CLOSE, BUT NOTHING HAPPENED. THEN WENT TO OPEN AND BACK TO CLOSE AND FINALLY CABIN ALT CAME DOWN. UPON LANDING CABIN ALT SHOWED 1,500FT AND HAD TO GO TO OPEN TO BRING ALT DOWN TO SEA LEVEL. MAINTENANCE FOUND AUTO MODE FAILED OPERATIONAL TEST PER TASK 21-31-00-702-001. REMOVED AND REPLACED CABIN PRESSURE CONTROLLER PER TASK 21-31-21-404-004. PERFORMED OPERATIONAL TEST PER TASK 21-31-00-702-001. OPS TEST GOOD.