A B737-300 DEPARTED AFTER CONTRACT MAINT INCORRECTLY WIRED AN AIR CONDITIONER RAM AIR DOOR IN THE CLOSED POSITION. FLT DIVERTED UNPRESSURIZED.

Narrative

ACFT LEGALLY DISPATCHED WITH R PACK DEFERRED INOP. ACFT HAD MAINT DONE ON IT IN ZZZ BY CONTRACT MECH FROM LCL FBO TO LOCK OPEN THE RAM AIR DOOR ON THE REMAINING GOOD PACK; AS THE DOOR WAS MALFUNCTIONING ON THE PREVIOUS FLT AND PROPERLY RPTED. ON CLBOUT OF ZZZ THE REMAINING PACK TRIPPED. THE ACFT IMMEDIATELY STARTED TO DEPRESSURIZE. THE CHKLIST WAS RUN AND THE PACK WAS UNABLE TO BE RESET BY THE CHKLIST. WE WERE NOW UNPRESSURIZED WITH NO AIR FLOW WHATSOEVER. WE ADVISED DEP OF OUR NEED TO DIVERT AND LAND DUE TO A PRESSURIZATION PROB. NEXT; WE CONTACTED DISPATCH BY VOICE AND ACARS AND IT WAS AGREED THAT WE WOULD DIVERT TO ZZZ1. MAINT WAS CONSULTED AND AGREED THAT AN OVERWT LNDG WOULD BE ACCEPTABLE AT OUR WT. DEP FACILITATED US INTO A DOWNWIND FOR RWY AT ZZZ1. AFTER ADVISING CREW AND PAX OF OUR SITUATION; WE MADE A NORMAL OVERWT UNPRESSURIZED LNDG AT ZZZ1. MAINT AT ZZZ1 DETERMINED THAT THE DEFLECTOR DOOR HAD BEEN WIRED (BY THE CONTRACT MECH IN ZZZ) IN THE GND OR DEFLECTED POS -- NOT THE OPEN OR FLT POS -- WHICH CAUSED THE PACK TO OVERHEAT AND FAIL. PAX DEPLANED AND A NEW ACFT WAS FOUND FOR THE FLT TO ZZZ3.