What was found
CLIMBING THROUGH FL 27 RED CARGO DOOR LIGHT ILLUMINATED. RED DOOR WARNING LIGHT AND AMBER HOOKS UNLOCKED LIGHT ILLUMINATED ON POWER MASTER CONTROL. LOUD BANG HEARD BEFORE RED CARGO DOOR ILLUMINATED. HIGH CABIN DIFFERENTIAL PRESURE (8) HAD TO CLOSE CABIN HEAT OUTFLOW VALVE TO MAINTAIN PRESSURIZATION AT 2,500 LIGHTS EXTINGUISHED. FOUND LEFT PRESSURE RELIEF VALVE OPENING AT (8.25) DIFFERENTIAL PRESSURE. REPLACED VALVE. CHECKED NORMAL PER MM 21-30-0. FOUND HOOK UNLOCK SWITCHES ON MAIN CARGO DOOR OUT OF ADJUSTMENT. ADJUSTED SWITCHED PER AERONAUTICAL ENGINEERS MM CHAPTER 5. OPS CHECK NORMAL. (M)