APU DEFERRED SO GND AIR IS USED TO START. FUMES ARE NOTED; BUT DISCOUNTED AS GND UNIT AS SOURCE. FUMES RETURN INFLT SO RETURN TO AN OVERWT LNDG IS MADE.

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APU AIR WAS INOP AND DEFERRED SO WE HAD TO USE A GND PNEUMATIC AIR CART TO START #2 ENG AT GATE. DOOR 1L WAS STILL OPEN WHEN THE MECH POSITIONED AND STARTED THE GND AIR CART IN ANTICIPATION OF STARTING #2 ENG. A STRONG IRRITATING ODOR ENTERED THE COCKPIT AND FORWARD CABIN AREA PRESUMABLY FROM THE OPEN DOOR 1L. I QUESTIONED THE MECH IF THIS ODOR WAS COMING FROM THE AIR CART; AND HE REPLIED THAT IT WAS. WE PROCEEDED TO START #2 ENG IN ORDER TO QUICKLY REMOVE THE AIR CART AND RESTORE CONDITIONED AIRFLOW TO THE CABIN AND COCKPIT FROM THE ACFT AIR CONDITIONING PACK. ONCE THE CABIN WAS SECURE AND DOORS CLOSED; WE PUSHED BACK AND PERFORMED A XBLEED START OF #1 ENG. AFTER BOTH ENGS WERE STARTED AND BOTH ACFT AIR CONDITIONING PACKS WERE ON; THE STRONG ODOR DISSIPATED. HOWEVER; SHORTLY AFTER TKOF AND DURING THE CLBOUT; THE ODOR RETURNED. I TOOK STEPS TO INCREASE COCKPIT AND CABIN AIRFLOW USING FLT MANUAL PROCS AND CALLED THE PURSER TO THE COCKPIT AND TO ASK IF SHE NOTICED IT ALSO. SHE COMPLAINED THAT IT WAS STRONG AND IRRITATING. I INSTRUCTED HER TO WALK THROUGH THE CABIN AND CHK HOW BAD IT WAS; AND SEE IF SHE COULD DETECT A SOURCE; IE; GALLEY OVENS; LIGHTS; AIR CONDITIONING DUCTS; ETC. HER ASSESSMENT WAS THAT THE ODOR WAS NOT DISSIPATING AND ACTUALLY GETTING WORSE. DECIDED TO RETURN AND LAND OVERWT RATHER THAN DELAY TO BURN OFF TO LNDG WT SINCE THE SOURCE AND TOXICITY OF THIS STRONG PERSISTENT ODOR WAS UNKNOWN. WE LANDED AT 153800 LBS WITH FULL FLAPS AND AUTOBRAKES (A320 MAX LNDG WT IS 142200 LBS). THE APCH; LNDG; AND RETURN TO THE GATE WERE UNEVENTFUL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR SAID THAT MAINT WAS UNABLE TO DUPLICATE PROB ON THE GND AFTER AN ENG RUN OF SEVERAL HRS. THE ACFT WAS RETURNED TO SVC. HE SURMISED THAT THERE MAY HAVE BEEN OIL IN THE DUCTING SYS FROM EITHER THE FAILED APU OR THE GND UNIT THAT WAS BEING BURNED OFF AND THIS WAS COMPLETED BY THE EXTENDED GND RUN OF THE ENGS AND AIR CONDITIONING SYS. NO FURTHER PROBS HAVE BEEN RPTED ON SUBSEQUENT FLTS.