As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR TURN BACK. ON REACHING CRUISE ALTITUDE, THE ACFT LOST PRESSURIZATION. ELECTED TO RETURN. NO EMERGENCY WAS DECLARED. ACFT LANDED WITHOUT INCIDENT. AFTER TROUBLESHOOTING, IT WAS DETERMINED THAT THE CABIN PRESSURIZATION WORKED NORMALLY WHEN NR 1 ENGINE BLEED IS DESELECTED. FOUND A BAD OVERTEMP SWITCH. REPLACED THE OVERTEMP SWITCH. REACTIVATED SOV. OPS CHECKED GOOD. ACFT RETURNED TO SERVICE.