What was found
T/O WAS PERFORMED ACCORDING TO OPTION NR 1 OF MEL 21-1 (RT PACK INOPERATIVE) AT 100FT WE SWITCHED LT A/C SYSTEM SWITCH TO AUTO & IT DIDN´T PRESSURIZE AIRCRAFT, SUPPLY PRESSURE DROPS TO ZERO CHECK LIST WAS PERFORMED & WAS UNSUCCESFULL THE WE SWITCHED THE PRESSURE CONTROL SYSTEM FROM AUTO 2 TO AUTO 1 AND THE FAULT REMAINED AT 10.000IN RNG VOR DURING APROACH THE LT PACK STARTER TO WORK. ACCOMPLISHED TROUBLESHOOTING REF AMM 21-20-00 PAG 121 PARAG. 3 - 4 FOR FLOW CONTROL VALVE DEFECTIVE SO WAS INSPECTED FLOW CONTROL VALVE FILTER. IT WAS FOUND CLOGGED.THEREBY WAS CLEANED AND WAS SWAPPED WITH THE RT FLOW CONTROL VALVE REF AMM 21-31-02.