A B767-200 WAS DISPATCHED IN NON COMPLIANCE WITH EQUIP COOLING VALVES LEFT OPEN AFTER TROUBLESHOOTING. FLT DIVERTED DUE TO UNABLE TO PRESSURIZE CABIN.

Narrative

ON 05/SAT/02; I WAS ASSIGNED TO WORK ON A B767-200 AT GATE XX. ONE OF THE ITEMS ON OUR OUTSTANDING DEFERRED MAINT ITEMS SHEET WAS A MAINT CARRY-OVER ITEM ABOUT A FORWARD EQUIP VALVE EICAS MESSAGE AND VALVE DISAGREEMENT LIGHT ON THE EQUIP COOLING SWITCH PANEL. THE MESSAGE AND LIGHT ILLUMINATED WITH EQUIP COOLING SWITCH PLACED IN STANDBY. WHEN SWITCH WAS PLACED IN AUTO POS; THE LIGHT AND MESSAGE WOULD GO OUT. THIS PROB WAS PUT ON DEFERRAL AND UNDER THE MEL 21-58-06 WAS DEACTIVATED BY PULLING AND SECURING A CIRCUIT BREAKER P11-3 P13; PUT EQUIP COOLING SWITCH INTO STANDBY POS; AND VERIFYING THAT THE FORWARD EQUIP GND SUPPLY VALVE AND FORWARD EQUIP OVERBOARD EXHAUST VALVE ARE CLOSED THEN PUT THE SWITCH INTO AUTO POS FOR THE FLT INTENDED. I TROUBLESHOT THIS DEFERRAL PROB USING THE FAULT ISOLATION MANUAL 21-58-00 AND PERFORMING AN EQUIP COOLING BITE ON THE AIR SUPPLY MODULE COMPUTER IN THE E&E BAY. ACCORDING TO THE FAULT ISOLATION MANUAL I NEEDED TO MAKE SURE A CERTAIN NUMBER OF CIRCUIT BREAKERS WERE IN THE CLOSED POS. ONE OF THOSE CIRCUIT BREAKERS WAS P13. I PUSHED IT IN AND DID A BITE CHK ON THE AIR SUPPLY MODULE COMPUTER. THE COMPUTER FAULTED GND SUPPLY VALVE V9 AND OVERBOARD EXHAUST VALVE V12. I HAD PLANNED ON CHANGING THE GND SUPPLY VALVE; BUT ALL OF ACR X VALVES WERE OTS AND WERE WAITING ON THE REPAIR VENDOR TO GET ONE BACK TO US. AFTER I PERFORMED THE BITE CHK; I WENT UP INTO THE COCKPIT AND PULLED AND COLLARED CIRCUIT BREAKER P13. I FINISHED UP MY PAPERWORK AND THEN LEFT THE AIRPLANE. B767-200 LEFT ZZZ AT XA00 FOR A FLT TO ZZZ1 WHEN THE PLTS NOTED THAT PASSING THROUGH 10000 FT; CABIN ALT WAS 10000 FT. THE PLTS DID AN AIR TURN-BACK AND LANDED BACK IN ZZZ. THE MECHS THAT WORKED ON THE AIRPLANE HAD FOUND THE ACFT WOULD NOT PRESSURIZE BECAUSE THE EQUIP COOLING VALVES WERE IN THE OPEN POS. THE MECHS PERFORMED THE PROCS OUTLINED IN THE MEL 21-58-06 PROC 2. THE EQUIP COOLING VALVES CLOSED AND THE AIRPLANE WAS RETURNED TO SVC. WHEN I PERFORMED THE BITE CHK ON THE AIR SUPPLY MODULE COMPUTER; I DID NOT REALIZE THAT THE COMPUTER GOES INTO A GND TEST MODE AND CYCLES THE VALVES. IT CYCLED TO THE OPEN POS. IT DIDN'T DAWN ON ME TO GO BACK AND CHK THE MEL TO MAKE SURE THE ACFT WOULD BE CONFIGURED FOR FLT BY HAVING THE VALVES IN THE CLOSED POS. WHEN I PUSHED IN THE CIRCUIT BREAKER P13 I ASSUMED NOTHING HAD CHANGED SINCE I HAD STARTED.