The Ac is blowing cold air out the driver's side of the 1999 Buick PA, but was blowing HOT air out of the right two vents. This car ha dual zone settings. The passenger side was set to cold also. Never seen this before. Later it stopped blowing HOT air, and was more like regular outside vent.

Check the actuator motor on the heater it directs the air into the vents. There is probably two of them be sure to check both. The motor makes the vents move and again directs the air where you want. Hope this helps.

Many Buick come with factory dual zone heat and air controles . . Check to see that both controlled are in heat mode

The actuator that 'blends' cold with hot is stuck in the cold position. There are a couple of options. Disconnect the battery, then drive the vehicle around without using the AC for 10 min, if the AC is defaulted to come on after a battery interuption, then shut the car down then turn it on again. You are trying to get the electronic actuator to reset and resume proper function. Another option is to try this: Start the car, adjust the pax side full hot, drivers full cold, wait 30 sec then shut car down, then start car back up and reverse the settings, pax full cold, drivers full hot. In both solutions, the vent actuators are stuck at either the full open or full closed, so you are trying to get it to 'self check' and allow them to resume proper function. After two years, I simply removed them altogether since I live where it is hot an only need cold.works just fine....

if it is dual zone climate control, then quite possible is the driver's side actuator or blend door.

My 02 Century has dual temp controls . One for driver for passenger. Make sure you don't have the dual climate enabled and just set for heat on your side and AC on the passengers

may have a bad blend door actuator.

You will need to replace the drivers side temp actuator. It is available at your local dealership.

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

broken cable? if possible trace the cables back to the box move then bolth and see if one doesnt, if so you could alwase manually move it for a temp fix