What was found
CRUISING AT FL370 RECEIVED AIR SYS OFF LEVEL 1, FOLLOWED BY AIR MAN NR 3 FAIL LEVEL 3. COMPLIED WITH CHECKLIST & LAND AT NEAREST SUITABLE. RELEASED FOR SERVICE IAW MEL 36-10-02-A. PERFORMED NR 3 PNEU SYS DECAY CHECK IAW AMM 36-00-04-5. 13 SECONDS FROM 30-20 PSI DECAY TIME. OK TO CONTINUE. REMOVED PANEL IMMEDIATELY OTBD OF NR 3 ANTI-ICE VLV PANEL. REMOVED NR 3 MANIFOLD DETECTION SWITCH IAW AMM 36-23-03-4 STEPS 1 THRU 2 A 6. AFTER REMOVING SWITCH NOTED SWITCH MOUNTING BRACKET IS CRACKED. INSTALLED NEW RT WING MANIFOLD FAILURE DETECTION PRESSURE SWITCH IAW MM.