heater problem 1991 jimmy - cold air only

Have new heater core and thermostat yet still blows only cold air. Anyone else have this problem? Winters on it's way and I need to get this fixed. Any thoughts would be appreciated.

1. Hot coolant circulating through it (not airlocked)?
2. Hot/cold selector cable attached to the lever/vent flap ?

the selector cable seems to be connected because the air does change.....it decreases in volume when set to heat though.
how would i check for an airlocked coolant hose? I imagine it should feel warm on the hose, on the engine side of the firewall.

all new to me.

and thanks Teaman3