As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING ENGINE RUN, L/H DUCT PRESSURE WAS 40 PSI AT IDLE, RT DUCT PRESSURE WAS 20 PSI, BOTH PACKS ON, ISOLATION VALVE CLOSED. GROUNDED - YES. REMOVED AND REPLACED #1 ENG HIGH STAGE VALVE AND HIGH STAGE REGULATOR REF B737-800 AMM 32-11-06 AND AMM 36-11-07. .