What was found
OXYGEN MASK INTERPHONE SYSTEM WILL NOT TEST ON GROUND. WILL NOT WORK WHEN SPEAKING DIRECTLY INTO OXYGEN MASK WITH THE PTT SWITCH IN THE "INT" POSITION. CAPT'S AND FO'S OXYGEN MASK INTERPHONE NOT WORKING. SWAPPED CAPTAIN & C SUPERNUMERARY, O2 BOX & MASK IAW AMM 35-11-51. OPS CHECK GOOD. SWAPPED F/O & L SUPER NUMERARY O2 BOX & MASK IAW AMM 35-11-51. OPS CHECK GOOD. L AND CTR SUPERNUMARY SEAT O2 MASK MICS DEFFERED IAW MEL ABX-25-25-3. A/C RETURNED TO SERVICE.