If heat comes out of the vents, but only when driving along, then i suggest that it may be the resistor pack. Its mounted inside the ducting, secured by a single screw with a 6-pin plug going to it. Unplug it and take it out. If its dead, then Toyota still sells them, but if only one coil has gone - then you may be able to repair it. If that still doesnt work, i can only surmise that the control panel has indeed died, or has loose/faulty contacts - in which case, i'll be looking for one myself if the resistor pack i just ordered doesnt work!
