I have a Toyota Highlander with 80,000 plus miles. Have a problem with my heat control knob. The heat will be on and if I hit a bump in the road or cross RR tracks it will blow cold air. It’s almost as if the bump shuts off the heat. If I reach over and turn the temp. knob from cold to hot the heat will kick back in. The fan knob works fine as well as the fan itself. Anybody else have this problem?
Many heater controls are vacuum actuated. Could be a loose or broken vacuum hose on the heat control that loosens up when you hit a bump.