Heat only flows from the front window vent

Hello, This vehicle uses electrical actuators to move the internal doors of the heater and ac (hvac) unit. There is an actuator for hot & cold; there is one for recirculation or outside air and another actuator that controls were the air comes out. This one is called the mode door actuator. The mode actuator or the hvac control head could be causing the issue. The mode door actuator is usually a less expensive part than the temperature actuator but can require more labor time to replace. Both can be check using a gm computer tool called the Tech2. We have this tool and would be glad to check it for you.