Toyota Highlander Heater issue

I have a 2002 Highlander V6 AWd with 80,000 miles on it. This summer there were a couple occasions when th a/c would blast out hot air and then switch back to cold if I played with the temp adjustment knob. Now, in the winter, it is doing the exact opposite, but much more frequently. Sometimes if I even hit a bump in the road it will switch to cold. So far, I have been able to coax the correct temp of air back. Part B of this is that there is no mid range heat - it is either fry your eyebrows off hot or Canadian winter cold. Anyone have any similar experience with this, any ideas, suggestions or resources?

It sounds like there’s a problem with the blend door control.

The blend door is what controls whether you want heated or cold air, or a combination of both. And this door can be controlled either by a vacuum motor or an electrical stepper motor. Sometimes removal of the glovebox will gain access to the blend door motor.