Remove the HVAC control unit. See if it's plug is melted, loose or the wire harness & pins are connected & locked into place.
Can also be the unit is finally going out. Open it up & see what's going on inside. If you do open it. Take before, middle & after pics.
Can also be the unit is finally going out. Open it up & see what's going on inside. If you do open it. Take before, middle & after pics.