As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMBOUT, RIGHT DUCT PRESS WAS SPIKING 10 TO 15 PSI ABOVE LEFT DUCT PRESSURE. DURING DESCENT, LEFT DUCT PRESSURE 10 PSI, RIGHT DUCT PRESSURE 30 PSI. GROUNDED - YES. REMOVED AND REPLACED HSR VALVE PER B737-900 AMM 36-11-07-000-801 & 36-11-07400-801. ACCOMPLISHED ENG BLEED AIR CROSSOVER OPERATIONAL TEST REF AMM 36-11-00-710-801 DUCT PRESSURES WITHIN LIMITS.