Air fan stays on after car turned off

Hello, You likely have a bad ignition switch or main relay. When the key is turned off, it turns off power to most items, including the A/C blower motor. It is very odd that it only blows from the defroster, but it should not have power to blow at all. Really interesting problem, and I'll look up the circuit to find where it could be getting power from. Do you every have issues with anything else in the vehicle staying on when the key is off and removed?