What was found
DEPARTED FROM BASE AND TURN ON BLEED AIR HEATING. IN CRUISE FLIGHT ABOUT 10 MINUTES INTO FLIGHT CREW MEMBER NOTICED HAZE DEVELOPING IN CABIN. COULD SMELL IT UP FRONT BUT NOT SEE IT. A FEW MINUTES LATER THE CAUTION SEGMENT LIGHT ILLUMINATED: HTG OVTEMP. LIGHT EXTINGUISHED LESS THAN 30 SECONDS AFTER TURNING SYSTEM OFF. ABORTED FLIGHT, RTB, CALLED MAINTENANCE.
MECHANIC SUSPECTED COMPRESSOR WASH REMNANTS STILL IN SYSTEM. FLEW AIRCRAFT WITH MECHANIC, DUPLICATED HAZE (UP FRONT THIS TIME) AND CAUTION LIGHT WHICH EXTINGUISHED IN 20 SECONDS AFTER SYSTEM TURNED TO LOWEST SETTING (NOT OFF). REFUELED AND RETURNED TO BASE WITH REOSTAT FULL ON BUT HAZE DRAMATICALLY DIMINISHED AND HTG OVTEMP DID NOT ILLUMINATE. RETURNED TO SERVICE AN HOUR LATER.