Heater core needs to be pulled out
Flip it upside down then shake it, you will most like hear coolant still inside because it is plugged up, replace it
Blend door is the COLD-HOT lever, just FYI, it is cable operated in 1994 models
If you open glove box and then fold it down all the way you can see Blend Door control with cable attached, move Temp Lever to make sure it is moving
When heater core is out you can feel the Door and test for movement as well
Vent control lever operates Vacuum "Motors", vacuum solenoids really, this has nothing to do with temperature control, thats a separate issue.
If lever doesn't move full range then something is wrong in that panel, probably need a new panel.
If lever moves but vent stays on Defrost then Vacuum reservoir or vacuum hose in engine bay is probably damaged.
Defrost Vent selection = no vacuum, so all vacuum "motors" are off
So if there is no vacuum coming from the engine bay at panel then Defrost is default
That lever selects vacuum hoses which open and close directional vent flaps when vacuum is applied or removed
On the passenger side of engine bay there will be a Black vacuum line coming from the firewall and it runs up to top Blower housing, to a Black Cylinder, thats the vacuum reservoir in a 1994.
Other hose on that reservoir should run to the intake manifold, it may have "T's" with other vacuum hoses, check them all for leaks
Pull off the line that goes to firewall and suck on it, it should hold pressure, no leaks