What was found
FLIGHT 7739, ENROUTE BIL-GTF. AIR TURNBACK PERFORMED DUE TO LOSS OF AFCS, APM FAULT AND EXCESS CABIN ALTITUDE ON CLIMB OUT. NO EMERGENCY DECLARED. MAINTENANCE CLEANED THE AIR VENTILATION VALVE AND OPS CHECKED THE PRESSURE CONTROL SYSTEM. OPS CHECKS OF AFCS AND APM, NO DEFECTS NOTED. SATISFACTORY OCF PERFORMED. AIRCRAFT RETURNED TO SERVICE.