B737-300 FLT CREW HAS FUMES IN THE COCKPIT DURING DEICING PROCS.

Narrative

WE RECEIVED ACFT LATE. AFTER LOADING PAX; I INFORMED THEM THAT WE WOULD HAVE TO BE DEICED (LIGHT SNOW FALLING AT MDW) AND THAT WE WOULD HAVE TO WAIT IN LINE TO BE DEICED. AFTER RECEIVING PUSHBACK AND TAXI CLRNC; WE GOT IN LINE TO BE DEICED. WHILE WAITING WE PERFORMED BEFORE DEICING CHKLIST. AT THIS POINT I ELECTED NOT TO TURN OFF THE #2 OR THE APU BLEED UNTIL LATER IN ORDER TO KEEP THE PAX AS COMFORTABLE AS POSSIBLE. WE THEN PROCEEDED TO BE DEICED. THE DEICING CREW INFORMED US THE TYPE OF DEICING FLUID TO BE USED AND THAT 2 TRUCKS WOULD BE WORKING US. WE CHKED THE HOLDOVER TIME AGAIN AS THEY STARTED SPRAYING US AND STARTED THE TIME. SECONDS LATER WE NOTICED THE SMELL OF DEICING FLUID. AT THAT TIME WE REALIZED MY MISTAKE AND IMMEDIATELY TURN OFF THE BLEEDS. SOME OF THE STEAM ENTERED THE ACFT INTERIOR. AT ABOUT THE TIME THE DEICING CREW FINISHED; THE FORWARD LAVATORY SMOKE DETECTOR SOUNDED. CALLED GND TO RETURN TO GATE; CALLED OPS AND MAINT. THEY MET US AND MAINT CAME ONBOARD AND CHKED THE ACFT; THEN SIGNED IT OFF.