ACR X TCASII TA RA WITH VFR ACFT EVASIVE ACTION DSCNT CLB. SEE AND AVOID CONCEPT.

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ACR X LEVEL 9000 FT HDG E; GIVEN 6000 FT AND A R TURN TO 160 DEGS. BEFORE WE COULD ACKNOWLEDGE CLRNC; ANOTHER ACFT READ BACK OUR CLRNC. DURING THIS TIME TCASII CALLED OUT 'TFC; TFC.' WE OBSERVED TARGET AT 11:30 POS ON TCASII 3 NM AND 300 FT BELOW. TCASII THEN SAID 'DSND; DSND' FOLLOWED IMMEDIATELY BY CLB; CLB AND THE GREEN DOTS ON THE VSI WERE AT 2000 FPM CLB. CAPT STARTED A CLBING R TURN. I TOLD APCH WE WERE RESPONDING TO A TCASII COMMAND AND WERE CLBING. I ALSO WAS TRYING TO FIND THE TARGET VISUALLY. UNFORTUNATELY; THERE WERE BROKEN CLOUDS IN THE AREA WHERE THE TFC SHOULD BE. AT 9400 FT TCASII SAID 'MONITOR VERT SPD' WHICH SAID LEVEL. I TOLD APCH WE WERE LEVELING AT 9500 FT AND ALSO HAD TIME NOW TO TELL HIM SOMEONE ELSE HAD ACCEPTED OUR CLRNC. AFTER HE GOT THAT STRAIGHTENED OUT WE WERE NOW READY TO COMPLY WITH THE ORIGINAL CLRNC. FREQ CONGESTION AT THIS TIME PREVENTED US FROM GETTING ALL THE INFO ABOUT THE TCASII TFC. AFTER LNDG IN PHL I CALLED APCH CTL AND THEY SAID THEY HAD A VFR TFC ABOVE THE TCA AT 8500 FT WBOUND AND WHEN THE CTLR WENT TO CALL OUT THE VFR TFC THE FREQ CONGESTION STARTED. HE DIDN'T SEE HIM CLB. TCASII WORKED AS ADVERTISED. WE CHOSE 9500 FT TO PREVENT TFC CONFLICT; WHICH I WAS TOLD BY APCH THERE WAS NO TFC CONFLICT.