What was found
SMOKE CAME OUT OF OVERHEAD VENT AT REAR OF COCKPIT FOR APPROX 5 SECONDS. JUST TURNED UP COCKPIT & COURIER TEMPS FROM 67 TO 74 DEGREES. DONNED O2 MASKS & TURNED DOWN BOTH TEMPS TO 70 DEGREES. FIRST SMELLED SOMETHING HOT & THAT PROMPTED US TO TURN AROUND. THE SMOKE NEVER CAME FWD TO OUR SEATS & IT WENT AWAY AFTER APPROX 10 SECONDS. RAN NR 1 & 3 PACKS FOR 20 MINUTES & DID NOT NOTICE ANY ODOR OR SMOKE. ALL TEMPS WERE IN LIMITS & CHANGED NR 1 & 3 COALESCER BAGS IAW MM 21-54-03-2. OK FOR SERVICE.