Eds95,
I just finished dealing with the same problem. Short of electrical problems in the control switches, the rest of the problems are vacuum related. The ‘motors’ under the dash are vacuum driven actuators, no 12 V here. In the absence of vacuum, the default settings are defrost for front, heat and floor for the rear.
First you have to determine if you have vacuum at the back of the control switch. Take the cover off the front to expose the 4 screws holding the panel with fan and temp controls. Take out the panel. On the back of the switch that controls the various airflow positions is a bunch of color tubes. The black one supplies the vacuum from the intake manifold. If you have a rear fan there is a Tee that divides the vacuum between the front and back. You can remove the block of color tubes from the switch for easier troubleshooting. After you start the engine, check for vacuum at the black tube. If there is none, you have to find out where is the block. Mine was between the Tee and the back of the control switch. After removing the junk with very thin wire and some brake cleaner, I used hard tube that comes with WD40 to reconnect the break in the black tube. Secure it with electrical tape.
If you have vacuum, then you have to chase it down to the actuators and between the different color tubes. 3 ft or so of a small tube that you can use for testing can help simulate vacuum at different points.
If you have a rear heater, you can check for vacuum by removing the small connector on the back of the rear control switch. There should be one black and one white tube. Once you have vacuum at the black tube and if the rear is still blowing hot, then you either have a leak in the white tube which changes color to green or there is a good chance that the switch is bad. This part is badly designed on the cheap by Ford. I had a bad switch. You can get new switch, or ‘fix it’ by disconnecting the actuator arm from the flap. You have to reconnect it for winter to get the heat back.
Hope this will help you a bit.
windtrak | 
