What was found
AFTER TAKEOFF THE AIRCRAFT WOULD NOT PRESSURIZE. ZERO PRESSURE ON BOTH PACK PRESSURE INDICATORS. NO MODE LIGHT ON TRP. AIR RETURN TO KSDF REQUIRED. WHILE AIRBORNE OUTFLOW VALVE WAS FULLY CLOSED WITH FLOW LIGHT ON PRESSURIZATION PANEL. NO FAULT LIGHTS ON EOAP. VERIFIED BOTH PACK SWITCHES WERE ON. AIR CONDITIONING SHUTOFF SWITCH TO OVERRIDE DID NOT HELP. NO AIRFOIL OR ENGINE ANTI-ICE WAS SELECTED ON. PERFORMED BOTH LEFT AND RIGHT PNEUMATIC HEALTH CHECKS PER WORK CARD 2120-2258 AND 2120-2277. ALL CHECKS WERE NORMAL. (LP# 8634350)