Dometec Briskair Duo-Therm Compressor won't quit running

Have you taken return air filter grille down at ceiling assy, & cleaned filter with dish soap & warm water? Check & see if you see little probe sticking out in behind there, and wipe it carefully as well, and make sure it's lined up to sense air flowing through there. Take a flashlight & look up into coils at front for lots of dust on them as well. Perhaps a thorough cleaning of all coils is in order if you say there's lots of dust, as choking airflow off with dust & dirt, will only shorten life of unit & use more hydro than necessary.