These pictures are from a 1997 Ford Econoline 250. 1997-1998 Econolines have a defective blend door that fails, resulting in loss of heater function. Ford will install a revised heater case (F7UZ-18478-CA) for $700 or more:
Adding a blend door manual control will solve the problem and can be done without removing the heater core.
Ford heater core and blend door before modification:
Motorized blend door actuator. This part didn't fail.
The failure occurs in the plastic connection between the actuator and blend
Drill a hole through the passenger side dash board above the blend door. Also drill a hole in the center of the blend door. Put a coat hanger or other wire through both holes. Bend the lower end of the wire so that it will lift the blend door when raised.
This photo shows the completed modification before reassembly. Lift the coat
hanger for heat. Lower the coat hanger when running the A/C.