No heat from blower

1990 C1500. No heat from blower. Fan works, thermostat seems fine. There's two lines on the top of the rad that are both hot after warm-up - a big one from the therm and a smaller one on the other end going to the core. The bottom big hose from rad to pump is cool, though. I thing it might have to due with actuator or door since I no longer hear the actuator when I adjust the heat, or it's quieter for some reason. Ideas on how to proceed?

If there is air moving when the blower is running, that resolves a couple of questions.

If both heater hoses to/from the core are hot, that resolves another couple of questions.

That really only leaves the blend door/dampers, and the controls for that. The temperature control in the dash is really only a potentiometer for most of that vintage GM vehicle.

https://www.youtube.com/watch?v=Gxxe7ZKfeIQ

1990 C1500. No heat... ...thing it might have to due with actuator or door since I no longer hear the actuator when I adjust the heat
Start with the actuator(s) you no longer hear.