AN ACR MLG CLBED IN RESPONSE TO A TCASII COMMAND.

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WE WERE APCHING KIAH TO LAND -- ASSIGNED A WESTERLY HDG AND AN ALT OF 4000 FT ON A MODIFIED DOWNWIND. THERE WERE 8-10 ACFT IN THE IMMEDIATE AREA. APCH CTL FREQ WAS VERY CONGESTED. WE WERE ADVISED OF AN ACFT AHEAD ABOUT 4-5 MI; NBOUND AT 3500 FT AND MANEUVERING VFR AT 3500 FT. WE HAD NO VISUAL CONTACT; BUT HAD A TARGET 400 FT BELOW US AT 12 O'CLOCK ON TCASII. AS WE FLEW CLOSER; THE TARGET TURNED YELLOW -- NO VISUAL CONTACT (UNABLE TO CONTACT APCH). THE TARGET TURNED TO RED; AN RA WAS GIVEN; I.E.; 'CLB; CLB.' WE CLBED TO PLUS/MINUS 4600 FT AND NOTICED A HIGH WING SINGLE ENG LAND ACFT AT OUR 3 O'CLOCK POS ABOUT 1/2 MI AWAY. WE TOLD APCH CTL AND DSNDED BACK TO 4000 FT. AFTER LNDG; WE CALLED ATC AND THEIR RESPONSE WAS THAT THEY DENIED RESPONSIBILITY SINCE THEY 'TOLD' US ABOUT THE TFC. THEY DIDN'T FAULT US FOR CLBING TO 4600 FT SINCE WE HAD A VALID RA AND RESPONDED IN THE CORRECT WAY IN ACCORDANCE WITH OUR TRAINING STANDARDS. THE MAIN 'TRIGGER' IN THIS SIT IS THAT THE SMA WAS 400 FT BELOW US ON TCASII WHICH IS WHAT OUR TCASII AND WE RESPONDED TO (REGARDLESS OF HIS 'ACTUAL' ALT).