Lets make sure both hoses are hot going to the heater core. Next lets listen and or see if the blend air actuator is moving. Not easy to get to since it is on top and next to the heater core. Sometimes the actuator fails and sometimes the blend door breaks.
let me know what you find
I would listen as the temp is switched back and forth from hot to cold for the actuator. Sometimes they make a clicking noise when they fail. Make sure when the actuator is out the door is ok, they break where the motor drives them sometimes.