Passenger side hot...Driver side cold

[Habanero]

An exhaustive search has turned up no answers, so I will try this route. I have an 87 SDL in which the A/C works great, but I seem to have a problem with the heat. I noticed this morning that the driver's side bottom vent is not blowing any hot air. The upper side vents are blowing hot air, as well as the passenger side floor vents. But, on my side there is only a slight, cool breeze and no sign of heat. My assumption is maybe a problem with the ducting, but I thought maybe I should check to see if anybody else has experienced a similar condition. By the way, this situation did not change no matter what setting the panel was on. Thanks in advance for any and all suggestions.