What was found
DURING CLIMB THROUGH 15000 FT. "CABIN ALTITUDE" LIGHT ILLUMINATED WITH MASTER CAUTION AND PASSENGER OXYGEN MASKS DROPPED. EXCECUTED CABIN ALTITUDE CHECKLIST & DESCENDED TO 14000FT. CABIN ALTITUDE INDICATED 12500 FT. WITH A DIFFERENTIAL OF APPROXIMITTLY 2.5 PSI. SECURED LT FLOWPACK FOR 1 MIN. THEN TURNED IT BACK ON. CABIN JUMPED TO 2000 FPM DESCENT & STABILIZED AT 500 FPM DESCENT. CABIN STOPPED DESCENT AT 5.4 PSI & WOULD NOT MAKE MAX DIFFERENTIAL. ACFT RETURNED TO BASE. MX TROUBLESHOT & FOUND RT ENGINE FLOWPACK VERY WEAK. INSTALLED OVERHAULED FLOWPACK & PNEUMOSTAT. ALSO FOUND SERVERAL LEAKS IN WING LE ON PNUMATIC LINES, CORRECTED AS REQUIRED. PERFORMED OPS CHECK FLT WITH NO DEFECTS NOTED. RETURN ACFT TO SERVICE.