AN EMB145 RETURNED TO THE DEP ARPT DUE TO THE INABILITY TO PRESSURIZE ACFT. THE PROCEDURE UTILIZED TO CONDUCT A PRESSURIZATION CHECK DID NOT INCLUDE STEPS TO REMOVE THE TEST CLIPS OR RESTORE THE AIRPLANE TO A NORMAL CONFIGURATION.

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I WAS ASSIGNED TO WORK ON ACFT X TO CLEAR SEVERAL OUTSTANDING MELS. THE ACFT HAD A HISTORY OF SHOWING AN 'ACCESS DOOR OPEN' MESSAGE ON EICAS. PLT RPTS: 'ON DSCNT AT 11000 FT; EICAS MESSAGE 'ACCESS DOOR OPEN' PRESENTED AND CONFIRMED ON DOORS PAGE. NO LOSS OF PRESSURIZATION. MESSAGE EXTINGUISHED WITHIN 3 MINS AT 6000 FT.' THIS ENTRY WAS DEFERRED PER MEL #52-7. THIS MEL WAS CLEARED AS FOLLOWS: 'FOUND CORROSION ON PIN 'F' OF CONNECTOR 2J7171. CLEANED CORROSION. OPS CHK GOOD.' ANOTHER PLT RPTS: 'DURING DSCNT OUT OF 15000 FT; EICAS MESSAGE 'ACCESS DOOR OPEN' CONFIRMED UNDER COCKPIT HATCH SHOWED OPEN. MESSAGE WENT OUT ABOUT 5 MINS LATER AT 11000 FT.' THIS ENTRY WAS DEFERRED PER MEL #52-7. THIS MEL WAS CLEARED AS FOLLOWS: 'REMOVED AND INSTALLED FWD ELECTRONIC COMPARTMENT DOOR MICROSWITCH. OPS CHECK GOOD.' ON THE NEXT FLT; PLT RPTS: 'FWD ACCESS DOOR OPEN INDICATION IN FLT. CABIN RATE AND ACFT RATE IS THE SAME.' THIS ENTRY WAS DEFERRED PER MEL #52-7; AND ALSO PRESSURIZATION AUTO AND MANUAL WAS DEFERRED AT THE SAME TIME PER MEL #21-18. AFTER REVIEWING THIS INFO; I FOCUSED ON THE FWD ACCESS DOOR INDICATION PROB. IT IS NOTEWORTHY TO MENTION THAT THE FWD AVIONICS DOOR GIVES ACCESS TO AN UNPRESSURIZED COMPARTMENT. THE PROB TOOK SEVERAL HOURS TO TROUBLESHOOT (I WORKED ALONE ON THIS DISCREPANCY); AND FINALLY WAS NARROWED DOWN TO THE FWD ELECTRONICS COMPARTMENT DOOR WARNING MICROSWITCH S7249 HAVING A HIGH RESISTANCE BETWEEN PIN A-4 AT DAU1 CONNECTOR J1021 AND GROUND POINT GS 0080 DC. AFTER REMOVAL AND INSTALLATION OF THE SWITCH; THE RESISTANCE WENT DOWN TO 0.6 OHMS; NORMAL. AT THIS POINT; ALTHOUGH MEL WAS NOT EXPIRING; MAINT CTL REQUESTED THE REPAIR OF THE DISCREPANCIES (TAT PROBE HEATING AND PRESSURIZATION) DUE TO WX ISSUES. THE PRESSURIZATION WAS MEL'ED BECAUSE OF THE DOOR INDICATION PIREP; AND THERE WAS NO PREVIOUS HISTORY IN THE LOGBOOK; I DECIDED TO PERFORM THE OPS CHECK OF THE PRESSURIZATION SYSTEM. DUE TO THE FACT OF BEING AT THE GATE AND VERY CLOSE TO DEP TIME; AS SOON AS I NOTICED AN INCREASE OF THE CABIN DIFFERENTIAL PRESSURE; MADE A JUDGEMENT CALL AND ABORTED THE TEST SATISFIED WITH THE OPERATION OF THE SYSTEM AND KNOWING THAT IS HAS NEVER BEEN WRITTEN UP AS A SEPARATE DISCREPANCY. AT THE SAME TIME; ME X; WHO CLEARED THE TAT PROBE MEL; HELPED ME OUT BY UPDATING THE MAINT HISTORY ENTRY FOR THE PRESSURIZATION DOOR DISCREPANCIES UNDER HIS EMPLOYEE NUMBER TO EXPEDITE THE RETURN TO SERVICE OF THE ACFT. AT THAT MOMENT AND BECAUSE THERE IS NO WRITTEN REFERENCE TO REMIND YOU; I DID NOT REMOVE THE OPENING DEVICE AT THE OUTFLOW VALVE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR EXPLAINED THE PURPOSE OF THE OUTFLOW VALVE CLIPS WAS TO PREVENT THE OUTFLOW VALVES FROM COMPLETELY CLOSING DURING THE MAINT MANUAL TESTING OF THE PRESSURIZATION SYSTEM. THE RPTR INDICATED THE PROC DOES NOT HAVE A DIRECTIVE AT THE COMPLETION OF THE TEST TO REMOVE THE TEST CLIPS OR RESTORE THE AIRPLANE TO A NORMAL CONFIGURATION.