What was found
IN CRUISE FLIGHT, UPON TURNING THE HEATER ON, SMOKE & FUMES FILLED COCKPIT AND CABIN. THE PROBLEM WAS SOME LT OVER RESIDUE FROM THE COMPRESSOR WASH. MECHANIC VERIFIED THE SYS INTEGRITY THEN RAN THE ACFT WITH THE HEAT ON AND DOORS OPEN TO VENTILATE SYS. RAN FOR APPROX 10 MINUTES, NO SMELLS OR SMOKE. TOOK ACFT FOR A SHORT FLIGHT TO VERIFY PROBLEM WAS CLEARED UNDER POWER. ALL WAS GOOD. RETURNED ACFT TO SERVICE RT AFTER THAT.