What was found
DURING CLIMB TO FL200 THE CABIN HI ALT MASTER WARNING LIGHT ILLUMINATED. THE CABIN RATE OF CLIMB INDICATED GREATER THAN 1000 FPM DONNED O2 MASKS AND DESCENDED TO 14,000. CYCLED LH & RH BLEED VALVES WITH NO CHANGE. ENSURED CABIN DUMP VALVE WAS CLOSED AND THE PRESSURE CONTROLLER WAS SET CORRECTLY. TESTED AIRCRAFT FLOW PACKS AND PERFORMED PRESSURIZATION CHECKS WITH PRESSURIZATION CART, ALL WITH NO DISCREPANCIES. REPLACED CABIN PRESSURIZATION CONTROLLER AND COMPLETED SATISFACTORY CHECK FLIGHT, TESTING FOR MAX DIFF AND INDIVIDUALLY CHECKING FLOW PACKS. AIRCRAFT RETURNED TO SERVICE.