Heater issue

Only my drivers side heat was working, the rest of the car blew cold air. I took apart the glove box and saw that the blend door actuator gear was shattered so I replaced that as well as the actuator. Now my issue is the gear on top won't stay in the position it needs to to blow hot air, so when I want got air I need to manually move the gear to backwards so the hot air will come through but it always eventually defaults back to the same position where it blows out cold. Picture attached.