As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE TROUBLESHOOTING POOR CABIN PRESSURIZATION, FOUND FAILED HOSE IN LEFT ENGINE AIR SUPPLY LINE TO CABIN. THIS CAUSED PRESSURIZATION TO WORK POORLY, BECAUSE THERE WAS NO INPUT TO CABIN FROM LEFT FLOW PACK. SUSPECT DUCT FAILED DUE TO AGE.