My wife’s Highlander AC and HEAT modes both work great separately - but it suddenly stopped letting anyone pick which! Instead it vacillates between heater and ac modes irregularly and often! Turning the fan motor or heat/cool selector knobs seldom make any difference. Sometimes a “bump” in the road or hard acceleration or deceleration seem to start the switching back and forth, but I haven’t found any reliable pattern. It might switch back and forth every few seconds, or it might behave for as long as 30 minutes! Are there some relays, motor valves or sensors to locate/test first, replace the entire climate control module, or take it to a dealer for them to ponder? Any recommendations would be appreciated!
Start looking on ebay for a replacement for your AC control unit, that is the thing which has the controls attached and goes in the dashboard.
I have the same issue with my 2005 Highlander.
Thanks Uncle Turbo! I’ll do just that!