What was found
FLIGHT 5305 - IAD-STL - IN CRUISE FLIGHT, GRAY SMOKE EMITTING FROM SIDEWALL VENTS WAS NOTICED SIMULTANEOUSLY BY BOTH PILOTS. DECLARED AN EMERGENCY, REQUESTED FOR AND RECEIVED VECTORS TO THE NEAREST SUITABLE AIRPORT, WHICH WAS EVV. THE FLIGHT ATTENDANT WAS NOTIFIED OF THE SITUATION AND GIVEN INFORMATION TO PREPARE FOR THE EMERGENCY LANDING. FOLLOWED THE -CABIN SMOKE OR FIRE- CHECKLIST. DURING THE LAST FEW MINUTES OF LANDING, SMOKE STOPPED AND WAS NO LONGER DETECTABLE. AT A COMPLETE STOP, NO FURTHER INDICATION OF SMOKE OR FIRE, EITHER FROM INSIDE OR FROM THE EMERGENCY CREWS OUTSIDE. MAINTENANCE FOUND NR 1 PACK ACM FROZEN. REMOVED AND REPLACED PACK NR 1 ACM IAW EMB 140 MM 21-51-03. OPS AND LEAK CHECK GOOD.