What was found
A/ICE DUCT WARNING MSG IN FLIGHT. LH FUSELAGE AND WING RED ON A/ICE SYNOPTIC PAGE. C/W QRH. STBY WORKS. LANDING WEIGHT 47,200 LBS, SMOOTH LANDING. ***AIRCRAFT REMOVED FROM SERVICE*** TROUBLESHOT PER FIM AND AMM 36-121-36-21. NO FAULTS FOUND SUSPECT FAILURE OF LEFT FIX SWITCH. R&R LEFT SWITCH IAW AMM 26-21-01 OPS/FUNCTIONAL TEST GOOD. OPS OF BLEED AIR SYSTEM IS GOOD IAW 36-21. REMOVED PLACARD/MEL