Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
Does the engine get up to operating temperature?
Is the coolant level full?
Is the system building up pressure?
yes to all questions
There could be a problem with the blend door actuator, (#6) but you may want to try flushing the heater core out to be sure that it's not clogged up.
Sometimes you can tap on the actuator with your finger tips and it may start moving again, (if that is the problem) but they are fairly hard to get to, (on top of the HVAC module)
Also, that the pressure is not too high in the cooling system, to where it cannot circulate.