For either the heater or A/C, the air vents only to the window defroster. The flow will not switch to the dash or to the feet. Any help?

The vents are vacumme controled. You may have a broken / disconnected vacuume line under the hood or dash. You could also have a bad mode switch or actuator. Check the lines and the canister first.

Mine did the same thing. If you follow the gear shifter to directly under the dash, close to the fire wall on the driver's side, there is a flap that is controled by a vacuum actuator. The flap has a plastic arm that extends down with a hole in it. The hole fits on to the silver bar that controls the flap. If you look under your dash, make sure it is connected together. Mine fell off, so I used a small rubber washer to keep it in place. To test it, look underneath your dash, while someone else is moving the control unit from vent to defrost. You should see the vacuum acuator arm moving up and down. Look to see if the silver-flap-bar is connected.