What was found
DURING CLIMB OUT AT FLT LEVEL 120, THE CABIN EXPERIENCED UNCONTROLLED PRESSURIZATION RESULTING IN THE CREW PERFORMING AN EMERGENCY DECENT. UPON SLOWING AIRCRAFT AND GEAR EXTENSION NORMAL PRESSURIZATION CONTROL WAS REGAINED. INSTALLED CABIN DIFFERENTIAL PRESSURE TRANSDUCER IN REPAIRED CONDITION. INSTALLED THE CABIN PRESSURE SELECTOR IAW AMM 21-02-03. OPERATIONAL CHECKS GOOD. NORMAL PRESSURIZATION WAS REGAINED WHEN AIRCRAFT PRESSURIZATION SYSTEM WAS CONFIGURED FOR LANDING IN MANUAL MODE, NOT WHEN LANDING GEAR WAS SELECTED.