1985 GS, no hot air. Coolant is topped off. Air is blowing from the vents. Air can be directed between face, feet and both. Thermostat was changed not too long ago, but can't swear to it's working. What do I need to be checking to get heated air in the cabin?

Thanks

 

Is the thermostat you changed the one in the heater/fan box in the passenger footwell?

 

It's a little awkward to see but if you stick your head under the driver side of the dash you should be able to seat the heater valve out the side of the center console.
Move the temperature control back and forth and see if the rod moves up and down. If it doesn't move it's not letting coolant flow into the heater core.
There's one plastic cover that may need to be removed.

Photo of the valve from another thread with the hoses removed: