What was found
ON INITIAL CLIMBOUT AN UNKNOWN ODOR/FUME BECAME PREVALENT IN BOTH THE COCKPIT AND THE CABIN. ALL CREWS EYES STARTED BURNING, NO SMOKE DETECTED OR OTHER CAS MESSAGES, ETC TO HELP DETERMINE ANY ISSUE. THE SMELL APPEARED TO BEGIN PERHAPS RIGHT AFTER THE APU WAS TURNED OFF THE BLEEDS WERE SWITCHED TO THE 10TH STAGE. WE RETURNED TO LAND QUICKLY AND THE SMELL WAS STILL ONBOARD UPON LANDING. CORRECTIVE ACTION: INSTALLED A NEW COALESCER BAG ON THE LH AND RH WATER SEPARATOR REF CL650 AMM TASK 21-51-13-160-801. PN: / 180849-28 NSN.