WITH AN AVIONICS VENT SYS FAULT MEL'ED AND AFTER RECEIVING AN ECAM AVIONICS SMOKE ALARM AFTER TKOF; AN A320 FLT CREW DELAYS THEIR RETURN LAND UNTIL SUFFERING A LOSS OF CABIN PRESSURE ON SID DEP FROM IAD.

Narrative

PRIOR TO DEPARTING THE GATE; WE HAD SEVERAL ECAMS REGARDING THE AVIONICS VENT SYS. ALSO THE #2 IRU HAD TO BE SWAPPED WITH THE #3. WHEN THE MECH OPENED THE AVIONICS COMPARTMENT WE GOT AN AVIONICS SMOKE ECAM. FINALLY GOT THAT CLRED AND THEN HAD A VENT SYS FAULT. WE WENT WITH THAT DEFERRAL AND THE INLET VALVE WIRED CLOSED AND THE EXTRACT FAN IN OVERRIDE TO BE RESET TO NORMAL INFLT. ONCE AIRBORNE; WE HAD A RETURN OF THE AVIONICS SMOKE ECAM. THE CABIN WAS CLBING THROUGH ABOUT 8000 FT AND THE ACFT WOULD NOT PRESSURIZE. MOVING THE EXTRACT SWITCH TO NORMAL HAD NO EFFECT ON THE PROB OF THE EXTRACT VALVE -- IT WOULD NOT CLOSE. AS THE CABIN PASSED THROUGH ABOUT 10000 FT; I DECLARED AN EMER AND WE NOSED OVER THE ACFT AT ABOUT 17000 FT. THE CABIN GOT UP TO ABOUT 11500 FT. WE DSNDED TO 10000 FT AND RETURNED TO IAD. WE LANDED ABOUT 700 LBS OVERWT WITH A DSCNT OF LESS THAN 200 FPM. HUMAN FACTORS: DID NOT BELIEVE WE ACTUALLY HAD ANY SMOKE (AND DID NOT PERCEIVE ANY). THE FO HAD A SIMILAR EXPERIENCE ON A RECENT FLT THAT WAS ABLE TO CONTINUE TO DEST SO WAS A LITTLE SLOW TO BELIEVE WE ACTUALLY HAD A PROB. SUPPLEMENTAL INFO FROM ACN 633309: MAINT WORKED FOR APPROX 45 MINS AND ENDED UP RELEASING THE ACFT WITH A DEFERRED EXTRACT VALVE IN OVERRIDE. EMER DECLARED.