2000 cadillac eldorado etc hot air drivers side and cold air passenger and system stops blowing on and offl. what could cause this?

SOURCE: A/C Blows hot on drivers side

driver's side temp actuator

SOURCE: Hot and Cold

The most likely cause of your problem is the blend doors under your dash. If they are not moving like they should it can cause this type of problem. You can look under the dash to see if there are any linkages that are disconnected. Some of these are very hard to change so you might want to take it to a repair shop unless you are very good with cars.

SOURCE: 99 STS AC is blowing hot air

I had the same problem but it was blowing hot air on the passenger side of the car. I assume you have the dual zone controls that I have as well. The problem is most likely the damper that controls the flow of hot and cold air into the car. The motorized component of the damper is most likely not working and its stuck in the hot air position.

I had mine replaced by a repair shop so I cant tell you how to replace it but it may be something that you can do if you have the time and patience to work on it.

Good luck

SOURCE: ac vents

One of the temperature actuators are not working it has 2, one for each side.

SOURCE: driver's side defroster and heater vents blow cold

The doors that open and close in the heater control unit are ran by motors. It sounds like a motor has quit in yours. When turning on the defrosters the motor closes the door to the heat for the floor