2005 Toyota Sienna heater problems

[Claypodie]

All of a sudden, I only get heat blowing on drivers side, all the other vents facing the passenger including the one blowing to the feet, plus all the rear vents, are blowing cool/warm air only. Took to Toyota dealer, and they have never run into this problem, and don't know what's up either. Cost me $85.00 to hear that.

What do I try next? Is there a vent door that may be stuck shut somewhere, not allowing hot air to blow to all the other vents? Do I have to remove dashboard to find out? Is there a drawing or schematic of some kind available that will show if there are doors that open close so I know where to start looking?

Any other advise?