A MAINTENANCE CONTROLLER REPORTS AN EMB-145 WAS NOT ABLE TO PRESSURIZE IN FLIGHT AFTER CONTRACT MAINTENANCE INADVERTENTLY SAFETY WIRED THE OUTFLOW VALVE IN THE 'OPEN' INSTEAD OF THE 'CLOSED' POSITION. AIRCRAFT DIVERTED.

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IN ZZZ; THE CAPT CALLED AND INDICATED THAT HE COULDN'T SET THE LNDG ELEVATION IN THE AUTO PRESSURE CONTROLLER. I DISCUSSED THE DISCREPANCY WITH MAINT CTL AND THE ELECTRO-PNEUMATIC OUTFLOW VALVE WAS SUSPECTED TO BE THE ROOT CAUSE. I DECIDED TO DEFER THE VALVE PER MEL 21-16 AND FAXED AMM REFERENCES EMB145 AMM TASK 21-31-03-000-801-A AND TASK 21-31-03-400-801-A WHICH ARE THE PROCS FOR THE REMOVAL AND INSTALLATION OF THE ELECTRO-PNEUMATIC OUTFLOW VALVE. THE PROCS FOR SECURING THE OUTFLOW VALVE ARE STATED AND ILLUSTRATED IN MEL 21-16. ALL THAT INFO WAS RECEIVED BY OUR CONTRACT MECH. WHILE CLBING TO 10000 FT; THE CREW NOTIFIED DISPATCH/MAINT THAT THEY HAD NO PRESSURIZATION. UPON LNDG IN ZZZ; LOCAL MAINT DETERMINED THAT THE OUTFLOW WAS SECURED INCORRECTLY. WITH COORDINATION BETWEEN THE CREW; DISPATCH; AND MOC; THE ACFT DIVERTED TO ZZZ. UPON LNDG IN ZZZ; I ASKED SUPVR TO CHK THE ELECTRO-PNEUMATIC OUTFLOW VALVE TO SEE IF THE CONTRACT MECH SECURED IT PER MEL 21-16. IT WAS SECURED IN THE WRONG POSITION. ZZZ MAINT CLRED THE MEL. THE CONTRACT MECH SECURED THE OUTFLOW VALVE IN THE OPEN POSITION; INSTEAD OF THE CLOSED POSITION. THIS PROHIBITED THE ACFT FROM PRESSURIZING. HE FAILED TO FOLLOW THE PUBLISHED PROCS THAT WERE PROVIDED TO HIM. THE EMB MEL REF 21-16 FIGURE 21-3 DETAIL 'A' SHOULD BE MORE CLEARLY DEPICTED AS TO WHERE THE SAFETY WIRE SHOULD BE SECURED. ADDITIONALLY; A NOTE STATING THAT THE BELLOWS SHOULD NOT BE DEPRESSED WHEN SECURING THE OUTFLOW VALVE WOULD HELP PREVENT THIS FROM HAPPENING AGAIN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THE CABIN PRESSURE CONTROLLER WAS NOT FUNCTIONING IN THE AUTO MODE; ONLY IN THE MANUAL MODE. PART OF THE MEL DEFERRAL PROCEDURE WAS TO SAFETY WIRE THE OUTFLOW VALVE IN THE CLOSED POSITION. BUT THE OUTFLOW VALVE ON THE EMB-145 IS NORMALLY SPRING LOADED CLOSED ON THE GROUND; AS COMPARED TO MANY OTHER AIRCRAFT WHERE THE OUTFLOW VALVE IS NORMALLY OPEN ON THE GROUND. THIS CONFUSED THE CONTRACT MAINTENANCE MECHANIC; WHO ENDED UP WIRING THE OUTFLOW VALVE IN THE OPEN POSITION; CONTRARY TO EMB'S MAINTENANCE MANUAL PROCEDURES AND DIAGRAMS. REPORTER STATED THE MEL REF 21-16 SHOULD BE MORE CLEARLY DEPICTED AS TO WHERE THE SAFETY WIRE SHOULD BE SECURED. ALSO. A NOTE STATING THE BELLOWS SHOULD NOT BE DEPRESSED WHEN SECURING THE OUTFLOW VALVE; WOULD HELP PREVENT THIS FROM HAPPENING AGAIN.