What was found
UNABLE TO MAINTAIN CABIN PRESSURE AT FL 330 WITH 0.78 MACH. REQUESTED FL 290 WITH SAME SET OF PWR. FLOW LIGHT REMAINED ON AND CABIN ALT CONTINUED INCREASING. NECESSARY TO SELECT ENGINE AND AIRFOIL ANTI-ICE DUE WEATHER CONDITIONS. CABIN RATE INCREASED AND NECESSARY TO REQUEST LOWER LEVEL AND RETURN TO FIELD. WITH POWER SETTINGS OF N1 86 PERCENT, CABIN CONTINUED INCREASING. AS PER MEL 21-1 CATEGORY C, RT PACK INOPERATIVE, ADJUSTED CLAMPS AND REINSTALLED HOSE IN ACM.