What was found
SMOKE IN CABIN & COCKPIT LANDED IN APPROX 2 MIN UNABLE TO DETERMINE CAUSE. EMERGENCY DECLARED. STARTED APU & RAN EACH PACK ONE AT A TIME, STARTED RT ENG SHUTDOWN APU AIR RAN PACKS USING RT ENG. PERFORMED SAME TASK ON LT ENG. NO SMOKE OR ODORS NOTED. PERFORMED POWER RUNS TO CHECK HP & LP ON ENGS. NOTHING NOTED. ACCESSED BOTH COALESCER SOCKS. NORMAL. REINSTALLED RAN APU WITH BOTH PACKS ON & FULL ELECTRICAL LOAD ON APU. NOTHING NOTED. MOVED ACFT INTO HGR. POWERED UP EVERYTHING, NO DEFECTS NOTED. CHECKED ALL C/BS, ALL NORMAL. CHECK BEHIND BOTH CO-PILOTS & PILOTS CB PANEL. NOTHING NOTED. CHECKED INLET & OUTLET OF ACM'S, CHECKED ACM'S FOR ROTATION BOTH TURN FREELY. ALL WORK IAW CE-750 MM.