As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT ENGINE AIR INLET INOP LIGHT CAME ON AFTER DEPARTURE. CYCLED 3 TIMES, STILL REMAINED INOP. RETURNED TO SFO. RAN LEFT ENGINE DEICE FOR 15 MINUTES AND CHECKED GOOD. PUT PSI GAUGE AT SWITCH, PRESSURE CHECKS GOOD. SWAPPED PRESSURE SWITCH'S FROM LEFT TO RIGHT AND RAN ENGINE. DEICE CHECKS GOOD. COULD NOT DUPLICATE.