These Duo Thermo Heat Pumps have a reverse switch/contact ?? that operates from air to heat and visa versa . This switch/contact can get stuck . Some stimes by putting the air on for a short period and shutting down for a short time and back to heat may help if it is a sticky switch/contact . Try this if you have not already replaced the unit . These units can not be repaired other than a good cleaning . Use a spray foam cleaner ; should be available at a good havac center . After removing the shroud on the roof , spray fins and any area that crud appears . Rinse with hose being careful not to flood that area of the roof , for otherwise water will come thru the ceiling inside . Clean or replace air filters inside . Been their , done this . or you will have to replace the unit as these are throw aways . Can be replaced yourself if you are some what handy , not a major project but time consuming. GOOD LUCK