The actuator that controls the diverter door needs to be replaced.
Check your settings...the passenger and drive have TWO different temperature settings.
Do you have dual control thermostats?
my 2000 Chevy venture van the air comes hot by drivers vet and cool by passenger vents
The heater core when air from the blower motor is blowing
heat and a/c barley blowing in back?
Car not blowing air or heat
It's because of the steering column. the passenger side of vehicle doesn't have the steering column so there is more room for ventilation. thus more airflow on the passenger side of the vehicle. there is still heat on the driver side but not as much.
I would guess the actuator on the drivers side is not working, take off the panel under the steering wheel. feel up under the dash to the arm of the actuator and pull it down to its bottom position, if this gives you heat, the actuator would seem to be the problem. Replace it a great expense and work, or drill a hole in the plastic arm, without breaking it, feed a piece of stiff wire through it and pull in down and tight, leave it that position if you have heat.
what i am assuming is being talked about is that when you go to turn on the heat in a Seville, heat will only be produced out of one side of vents. there are a number of valves in a Seville which control wether the air that is coming out of the vents in hot or cold. in a Seville there are a pair of these valves one for the passenger side air, and one for the driver side air. the reason why only one side of the car is blowing hot air is because one of these valves has gotten stuck in the "cold air" position and needs to be replaced. the same thing happened on my car but the drivers side was the one not blowing heat.
What do you mean by "has no heat"? No air blowing out, blowing out cold air when heater is on, blowing nothing at all? Heater not turning on? What specifically is happening?
Try completely disconnecting the battery for 1 hour then reconnect it. That should reset some door that controls the airflow. I just experienced hot air blowing on the pass side and cold air on the drivers side. I did the reset and now I have heat on both sides. Hope it works for you.
The problem is in the controler. TAke it to the dealer. The problem is likely one of the 5 actuators under the dash. There is one for the passenger and one for the drivers side. When you move the temp setting, you should hear them moving. If not, one may need adjusting or replacing.