What was found
CABIN ALT WARNING CLIMBING THROUGH FL270, CABIN ALT SHOWED 10,000, CLOSED CARGO HEAT OUTFLOW VALVE, NO CHANGE IN CABIN ALTITUDE. PERFORMED QRH CABIN ALT WARNING CHECKLIST. THEN PERFORMED FAILURE OF PRESSURIZATION OF CONTROL CHECKLIST. SYSTEM WOULD NOT PRESSURIZE IN AUTO OR STBY. IT DID WORK IN MANUAL. OUTFLOW VALVE INDICATED FULL CLOSED IN AUTO AND STBY MODES. REMOVED AND REPLACED PRESSURE CONTROLLER PER M/M 21-31-010-4. PREMATURE REMOVAL/INSTALLATION, OFF MFG 790960-1, SRL 8711490, ON MFG 790960-1, SRL 79K3611.