What was found
AC HAD BEEN PARKED FOR APPROX 2 WEEKS ON RAMP IN A TROPICAL CLIMATE. WHEN FLIGHT CREW CONDUCTED THEIR PREFLIGHT INSPECTION, IT WAS NOTED THAT THE O2 SYS QTY WAS INDICATING 0 PSI ON EICAS AND DIRECT READING GAUGE ON EXTERIOR OF AC. SERVICING OF O2 SYSTEM WAS ATTEMPTED, HOWEVER PRESSURE REMAINED AT ZERO. UPON FURTHER INVESTIGATION IT WAS DISCOVERED THAT LINE INSTALLED UNDER PILOTS SIDE CONSOLE CONNECTING THE PILOTS OXYGEN MASK BOX TO OXYGEN SUPPLY WAS RUPTURED AT END FITTING (HOSE HAD COME UN-SWEDGED). A REPLACEMENT LINE WAS ORDERED FROM MFG AND INSTALLED IAW AMM. AS PRECAUTION O2 CYLINDER REPLACED WITH SERVICEABLE UNITS AND O2 SYSTEM WAS PURGED IAW AMM. AC WAS THEN RELEASED FOR SERVICE.