What's wrong when my 2003 Toyota Highlander blow cool air through the vents when I turn the heat?
The "mixer" vent may not be changing position ... this can be caused by a broken vacuum line, a bad vacuum actuator or a bad temperature regulator
Mine does the same thing I have a 2003 Highlander also. I just either give the engine a chance to heat up or turn the temp knob up one or 2 notches and usually that works. It's a pain, but haven't been too concerned to get it checked out.
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