As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PER INBOUND ACARS PILOT REPORT (FLT 816): AT FL350 R DUCT PRESS 40 PSI LEFT DUCT PRESS 20 PSI. GROUNDED - YES. ACCOMPLISHED B737-800 FIM 36-10 TASK 804 STEPS F 32 & 33 (REMOVED AND REPLACED 450 F THERMOSTAT & PRECOOLER CONTROL VALVE SENSOR ON #1 ENGINE).