What was found
DUCT PRESS INDICATION SHOWING 25PSI DIFFERENTIAL, LEFT 18PSI, RIGHT 43PSIIN CLIMB AND CRUISE, IN DESCENT LEFT AND RIGHT HAD A SPLIT OF 8PSI. GROUNDED - YES. WHILE ACCOMPLISHING T/C NG-36WC-00001 FOUND BLEED AIR REGULATOR TO BE BAD. REMOVED AND REPLACED BLEED AIR REGULATOR REF B737-800 AMM 36-11-03-400-801. OPS CHECK GOOD. NO LEAKS DETECTED. COMPLETED TASK CARD # NG -36WC-00001 AND PERFORMED BLEED AIR CROSSOVER OPERATIONAL TEST WITH NO DEFECTS PER AMM 36-11-00-710-801.