OK the actuator is located on the right center on top of the heater box. If you drop the glove box all the way down, dump the excess junk, that's what I see all the time. Any way if you look toward the left at the center, there will be an actuator, plastic box, bolted to the top of the heater box. The space between has a black rod at a right angle wrapped around the control door rod. While adjusting, with the key on, the hot to cold control, the rod should turn back and forth slightly while changing the door from heater to A/C. Let me know.
I had to look back; As I commented on the first post, "if the coolant is full and the heater core is hot", it could be your heater core. Have you not had your heater core checked. You had a radiator and thermostat installed, for whatever reason, and the heater core could be restricted. I'm only 70 miles away from you, and would/could have made your heater work for less money.
In my experience, the blend door actuator is broken. When you activate your heater, the blend door rotates to direct the air through the heat exchanger to warm/heat the air. There are plenty of instructions online for do-it-yourselfers. If you have it done by a shop, it will be expensive, the parts are cheap, but it is labor intensive.