B737-300 DSNDING TO FL290 TO HOLD FQM. AT FL300 BEGAN TO LOSE CABIN PRESSURE. SOP FOLLOWED AND CABIN CONTINUED CLB TO 13000 FT. STARTED EMER DSCNT TO 10000 FT AND ADVISED CTR OF PROB. CLRED DIRECT EWR AND DSCNT TO 10000 FT. WHEN IN LEVEL FLT AND THRUST ON THE ENGS; COULD MAINTAIN CABIN PRESSURE. LANDED EWR OK. FOUND DOOR SEAL BLOWN AND E&E COMPARTMENT VALVE NOT SEALING. NINTH STAGE HIGH PRESSURE AIR SAFTIED CLOSED; CANNON PLUG FOUND OFF FOR #2 PRESSURIZATION. ONLY AIR FROM #1 ENG FIFTH STAGE.

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ON INITIAL DSCNT INTO EWR; CLRED TO FL290 FOR HOLDING AT FQM VOR. NEAR FL300 CABIN BEGAN CLB. APCHING 10000 FT; SELECTED STANDBY MODE OF OP FOR PRESSURIZATION -- NO HELP. WENT TO MANUAL AC OUTFLOW VALVE FULL CLOSED. WENT TO MANUAL DC. TOLD ATC WE HAD LOST OUR CABIN ALT AND REQUESTED 10000 FT. WE CONTINUED DSCNT. CABIN ALT REACHED ABOUT 13000 FT; SO OXYGEN MASKS DID NOT DEPLOY. AT 10000 FT WAS GIVEN 9000 FT. WE HAD NOT DECLARED AN EMER AS CABIN WAS NOW STABILIZING. CTR WAS ADVISED THAT TO KEEP EVERYTHING IN ORDER WE WOULD DECLARE EMER. CTR SAID THEY HAD ALREADY DECLARED THE EMER AND WE WOULD BE CLRED DIRECTLY TO EWR. DURING THE REMAINDER OF FLT WHENEVER PWR REDUCED; CABIN BEGAN A CLB. VERY LITTLE CTL OF CABIN DURING REST OF DSCNT. LNDG; UNEVENTFUL. FLC OXYGEN WAS USED FROM FL300 DOWN TO 10000 FT. FLT ATTENDANTS DID NOT USE OXYGEN AND NO MASKS WERE DEPLOYED. CABIN DID NOT GO ABOVE APPROX 13000 FT. PAX DID NOT COMPLAIN AND NO INJURIES. MAINT EWR FOUND DOOR SEAL BLOWN OUT; AND E&E COMPARTMENT VALVE NOT SEALING. HAD MEL OF #1 ENG ANTI-ICE VALVE WIRED FULL OPEN. NINTH STAGE HP AIR SAFETY CLOSED. CANNON PLUG FOUND OFF FOR #2 PACKS; SO ONLY AIR WAS FROM #1 ENG FIFTH STAGE. WHAT A COMBINATION! SUPPLEMENTAL INFO FROM ACN 354630: TURNS OUT THAT WE WERE ONLY GETTING #1 ENG SINGLE BLEED AIR IN THE LOW FORMAT FOR PRESSURIZATION. STANDBY PRESSURIZATION CTLR; MANUAL AC-DC TRIED WITH NO CORRECTIVE RESULTS.