I have a 1998 Lx470 and the other day i had 8 people in there and they turned the rear heating on but for some reason the rear passenger side vent only blow cold air even if you change the heat all the way up. So the vents by the passenger seats and the seats all the way in the back all blow cold air i looked at all the fuses and all look fine. Is there something i am not doing right ? what could be the problem? thanks