ACR RETURNS TO LAND WITH FUMES IN COCKPIT AND CABIN. PREVIOUS MAINT DISCOVERED TO BE THE PROB.

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ON TKOF ROTATION THE CREW NOTED A STRONG ODOR ENTERING THE COCKPIT. THE ODOR HAD AN UNUSUAL; SEMI-ELECTRICAL SMELL BUT SEEMED TO BE ENTERING THE COCKPIT THROUGH THE AIR CONDITIONING SYS. FLC SEARCHED COCKPIT FOR SOURCE OF ODOR AND PRESENCE OF SMOKE. THE SOURCE COULD NOT BE ASCERTAINED AND NO SMOKE WAS FOUND. CABIN CREW WAS CONSULTED WHO RPTED NEGATIVE SMOKE BUT DID ACKNOWLEDGE THE ODOR AND INDICATED THAT IT WAS COMING FROM BEHIND HER; MEANING THE COCKPIT. THE CREW DECIDED TO RETURN TO THE DEP ARPT TO MAKE A PRECAUTIONARY LNDG. COMPANY FLT CTL AND ATC WERE NOTIFIED OF OUR INTENTIONS TO RETURN AND LAND. ATC WAS TOLD THAT WE HAD 'FUMES' IN THE COCKPIT AND WE WERE RETURNING. ATC ASKED IF WE NEEDED GND ASSISTANCE. WE RESPONDED THAT NO ASSISTANCE WAS REQUIRED AT THE PRESENT TIME. WE WERE VECTORED TO DOWNWIND; AT WHICH TIME ATC REQUESTED THE NUMBER OF SOULS ON BOARD AND THE FUEL REMAINING IN LBS. THE CREW READIED THE OXYGEN MASKS BUT DID NOT DON THE MASKS AS NO SMOKE WAS PRESENT AND THE ODOR WASN'T IRRITATING THE CREW. NORMAL CHKLISTS WERE COMPLETED AND LNDG WAS UNEVENTFUL. CFR VEHICLES MET THE ACFT AS WE EXITED THE RWY. THE ACFT WAS STOPPED AND THE CREW AGAIN SEARCHED THE COCKPIT FOR THE SOURCE OF THE ODOR. ONCE AGAIN WE WERE UNSUCCESSFUL. WE RETURNED TO THE GATE AND THE PAX WERE DISEMBARKED. THIS WAS THE FIRST FLT FOR THE ACFT OUT OF OVERNIGHT MAINT. THE ACFT MAINT LOG WAS CONSULTED AND IT WAS DISCOVERED THAT MAINT HAD PERFORMED A COMPRESSOR WASH/BLEED LEAK TEST THE PREVIOUS NIGHT. MAINT PERFORMED A RUN-UP SUBSEQUENT TO OUR RETURN AND FOUND THAT THE ODOR OF RESIDUAL COMPRESSOR WASH FLUID WAS ENTERING THE CABIN THROUGH THE AIR CONDITIONING PACKS. MAINT PERFORMED GND RUNS TILL ODOR WAS PURGED AND THE ACFT WAS RETURNED TO SVC THE NEXT DAY. AS FAR AS THE CREW'S HANDLING OF THE SIT IS CONCERNED THE DECISION TO USE OR NOT TO USE OXYGEN WAS A JUDGEMENT CALL. IN LIGHT OF RECENT ACCIDENTS; THE CREW RESPONDED SECONDS AFTER TKOF WITH A QUICK DECISION TO RETURN TO THE DEP ARPT. WE WERE BACK ON THE GND IN LESS THAN 5 MINS AND ABLE TO MAKE AN EMER EVAC SHOULD THE ODOR DEVELOP INTO SMOKE AND A FIRE. ON THE OTHER HAND; HOWEVER; UPON FURTHER EXAMINATION OF OUR EMER CHKLISTS WE DISCOVERED THAT OUR 'SMOKE -- AIR CONDITIONING' PROC SHOULD BE RUN FOR NOT ONLY SMOKE BUT ALSO ODORS IN THE COCKPIT. ANOTHER CHKLIST WE HAVE IS A 'SMOKE REMOVAL' PROC DOESN'T MENTION THE PRESENCE OF ODORS. SINCE WE WERE UNABLE TO DETERMINE THE SOURCE OF THE ODOR WE WOULD HAVE OPTED FOR THE MORE GENERAL SMOKE REMOVAL PROC. EITHER PROC WOULD HAVE HAD US FIRST DON AND USE OUR OXYGEN MASKS. AT THE TIME THE ODOR SEEMED TO BE MORE OF A NUISANCE THAT A THREAT. IN HINDSIGHT; HOWEVER; ANY ODOR SHOULD BE TAKEN SERIOUSLY AND ODORS/FUMES CAN BE TOXIC. THERE IS A HESITANCY TO USE THE MASKS DUE TO THEIR CLUMSINESS BUT THEIR NEED/BENEFIT SHOULD BE WEIGHED HEAVILY AGAINST THE NEED TO LAND.