Am I glad to see you talking about this. I have a problem regarding this as well. My heater only works on lever 4 (max) either hot or cold. the direction for it to flow is good on all levels (feet, body, windshield etc). What should I change because people keep telling me it`s from the command switch, but other people tell me that it`s from the picture Siruncle posted, and that those 4 metal things are gone and should be replaced ?
Have a look up above the accelerator pedal, you should see the resistor pack. Usually if it has failed the connector melts, the good news is, they are cheap to replace. If the wiring has melted too, you'll need some loom too.
Ford will sell you the part, and a length of loom with a connector on it for you to join onto your car.
Alternatively, go to the breakers yard, find yourself a ford car, (in similar aged fiesta, escort, mondeo) and have a look in the same place, Most of these will fit the mondeo, and the loom bit is the same too. Take plenty of loom.
I believe the later type are better, so try and find one of those, (bottom of the two in my previous post)