No heat in vehicle changed heater core what could be the problem?

changed the heater core have heat at the heater core but its not blowing hot air inside the vehicle|||Divert-er door Or the door that opens and allows the heat to enter the car.|||thermostat?|||if it isnt blowing any air at all it could be a fuse or the fan motor. if it is blowing air and it is cold it could be the thermostat or divertor door