What was found
AT 1200 MSL, NOTED THAT THE AIRPLANE HAD ALREADY DEPRESSURIZED WITH PROPER FIELD ELEVATION SET. REMOVED FROM SERVICE. COMPLIED WITH FIM 21-30-00-810-804, PARA 1 - 3 A(2), TESTED IAW TASK 21-31-00-720-801. TEST FAILED, WOULD NOT PRESSURIZE IN AUTO. NO FAULTS REPORTED BY PILOT, NO FAULTS FOUND IN CDS, COMPLIED WITH FIM 21-30-00-810-814, FUNCTIONAL TEST OF PRESSURIZATION CONTROL OPERATES AS DESCRIBED IAW AMM 21-30-00-720-801. IN AUTO AND MANUAL. CABIN PRESSURE CONTROLLER REPLACED AS A PRECAUTION. AIRCRAFT RETURNED TO SERVICE.