As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF, VISUAL SMOKE WAS OBSERVED IN THE COCKPIT AND CABIN COMING FROM AIR CONDITIONING VENTS. AIRCRAFT RETURNED TO FIELD AND LANDED WITHOUT FURTHER PROBLEM. PROBLEM COULD NOT BE DUPLICATED ON GROUND. TEST FLIGHT CONDUCTED AND FLIGHT WAS SATISFACTORY. AIRCRAFT RETURNED TO SERVICE. NO FURTHER PIREPS THROUGH 071796. APU WAS PLACED ON MEL, THE PREVIOUS FLIGHT FOR THE SAME PROBLEM.