What was found
AFT F/A SAID ITS COLD IN AFT PORTION OF CABIN. DUCT TEMP AT 20-22C W/ AFT CABIN TEMP SHOWING 30-32. TEMP KNOB MOVED TO 3-4 O`CLOCK POSITION WITH NO INCREASE IN HEAT. DISCUSSED W/ MX CONTROL VIA SAT COM. POSSIBLE AFT CABIN TEMP PROBE FAILURE/ CONTAMINATION. ACFT GROUNDED. ACCOM. FIM TASK 21-61, TASK 857, FOUND AFT CABIN TEMP. SENSOR ASSY FILTER BLOCKED. CLEANED FILTER IAW AMM TASK 21-61-06-100-801. PERFORMED REPAIR CONFORMATION WITH TRIM AIR ON IN ALL TEMP. CONDITIONS TEMP. IN CABIN AND ON INDICATOR WAS APPROXIMATELY THE SAME. NO FAULTS NOTED.