What was found
F/A REPORTED SMOKE COMING FROM FLOOR VENT AT ROW NR 7 WHILE CLIMBING OUT AT 400 FT WITH BOTH PACKS OPERATING OFF APU. F/A DESCRIBED SMOKE AS "THICK AND GREY" MOVING ACROSS AISLE. CREW ELECTED TO DECLARE EMERGENCY AND AIR RETURN BACK TO EWR WITHOUT INCIDENT. MX PERFORMED FIM TASK 21-20-00-810-801-A AND FOUND DUCT FOR AMBIENT TEMP SENSOR BOX ASSY AND AFT HOSE FOR RECIRCULATING FAN NR 2 DISCONNECTED. MX REATTACHED BOTH DUCTS AND R & R THE AMBIENT TEMP SENSOR WITH OPS CHECK GOOD. ACFT WAS APPROVED FOR RETURN TO SERVICE.