Why does my heat stay on defrost all the time. Duel control doesn't work. Vent control doesn't work too. Wy?
check for a vacuum leak...
If your is digitally controlled you may have a failure in the main control unit, it is uncommon that every position has failed on a digital unit. However if it is manual control then Kelly is spot on about loss of vacuum, on a manual unit when vacuum is lost default mode is defrost.
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