Yes, samurais heat only comes from the defrosters and the lower vents. The lower vents are literally right off the heater core so it is impossible to not have heat one one side of the truck there. On the upper vents, defrosters, I guess it can be possible. Just look at yout heater box and make sure that the tube that runs up to those vents is attached and such. Another thing to check is on the ds side of the box, an old sammi trick is to cut a hole in the box and vacuum off the heater core to get rid off all the debris that falls in there. Just take a look and if you have a hole make sure it is sealed good with some duct tape or similar. Prolly half the sammis that I see have this"mod" done, so something to look into