No heat

I have a 99 DeVille. During the summer, the AC vents on the drivers' side blew out warmer air than the passenger side. Now that the heating season is here, the heat vent on the floor blows out cold air on the drivers' side and warmer air on the passengers' side. I have replaced the thermostat and the coolant is full. Is there a possibility that there is an outside vent stuck open and if so how do I check for this? Also, what is the fix for it?

Hey 99: Not sure if your wheels will have the same system as mine but here is what I did. You have to take out the glove box liner and in behind there you will see a cover for the heat/cooling chamber. Snap it open and you will see the electronically controlled air mix door. On mine the hinge was rusty and wouldn't let the door go fully closed. Use some WD-40 or similar product and free up the hinge. Make sure the door is then going through the full travel and then turn on the ignition to check the functions via the heat/air controls. The small servo motor that does this function is not very powerful so every thing has to be easy to move. Hope this helps, chow,Don.

Thanks Don. I'll give that a try this weekend. I hope it works. It's getting pretty cold here in Ohio. If I can't fix it I can always let my wife drive it.