As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AUTO PRESSURIZATION BECAME VERY ERRATIC DURING CLIMBOUT. RETURNED TO SFO. DEF AUTO PRESSURIZATION AS PER MEL 21-31-1A CW MX PROCEDURE PER MEL APPX A. VALVE SAFTIED CLOSE. REPLACED ELECTRONIC CONTROLLER IAW EMB 120 MM 21-30-01. OPS CHECK GOOD. (P/N ON 22201T011400) (S/N ON 164) (S/N OFF 518).