Where is the Blend door located?

On a 1992 the blend door doesn't use an actuator it uses a cable that goes from the slider to the blend door itself. The common failure is the plastic tab on the control head, it breaks, and the cable no longer is held in place and instead it moves with the lever. The first item to check though is the heater control valve under the hood, it is vacuum controlled and if the line came off or the diaphragm fails you get no hot water through the core. If the valve is opening the heater hoses will get hot at the same time, if it's closed the hose on one side of the valve will get hot and the other side only gets warm.

The diagram I posted won't show the valve as it's in the coolant hose between the engine and the heater core. Follow the heater hoses and you should find it, but if the hose at the inlet is hot then the valve should be open and that would show a blocked core. You could try reverse flushing it to see if you can clear the core out.