CAPT OF AN ACR MDT ACFT ELECTED TO PARTIALLY PRESSURIZ THE ACFT EVEN THOUGH THE ACFT WAS 'MEL-ED' FOR NON PRESSURIZATION FLT DUE TO A LEAKY MAIN CABIN DOOR SEAL.

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ACFT HAD AN MEL THAT PAX DOOR SEAL WAS LEAKING AND SHOULD NOT BE FLOWN IN PRESSURIZED FLT. ACFT WRITE-UP STATED THAT WHEN DIFFERENTIAL PRESSURE ROSE ABOVE 1.5 DOOR SEAL WOULD LEAK; INOP SIGN WAS ON PRESSURE CTLR. THE CAPT ELECTED TO FLY PRESSURIZED AND WHEN CLBING THROUGH 4000 FT DOOR SEAL STARTED LEAKING. FLT ATTENDANT NOTIFIED CAPT OF SUCH AND HE ELECTED TO DECREASE DIFFERENTIAL PRESSURE (2.5 BACK TO 1.6) AND CONTINUE CLBING TO 8000 FT. I TOLD HIM THAT IF HE WISHED TO DO THIS HE SHOULD AT LEAST STOP HIS CLB AT 6000 FT OR LESS TO DECREASE DIFFERENTIAL PRESSURE AND THE LOUD NOISE THAT COULD BE HEARD THROUGH THE INTERCOM. HE ELECTED TO CONTINUE THE CLB AND CONTINUE TO DECREASE DIFFERENTIAL TO 2.0. THIS DID DO AWAY WITH A LOT OF THE NOISE; BUT NOT ALL. DO NOT THINK ACFT SHOULD BE PRESSURIZED AT ALL WHEN KNOWN PRESSURE LEAK IS DISCREPANCY. ACFT FLTS THAT ARE SCHEDULED SHOULD BE FLOWN AT REDUCED ALTS. FLT ATTENDANT STATED DURING AND AFTER FLT THAT MUCH PAX CONCERN AND DISCOMFORT WAS EXPERIENCED.