I have a 2000 Buick Regal.
The Heater/Air Conditioner runs erratically. Sometimes when set for air conditioning it will blow hot air out on both passenger and driver sides, sometimes hot air on one side and cold air on the other side, and sometimes it will run just perfectly. Same thing when on the heat setting, sometimes blows cold air on both sides, sometimes cold on one side and hot on the other side, and sometimes runs just perfectly. I have had it back to the dealer several times and they have replaced the entire unit in the dashboard, but weeks later the problem just reappears.
Does anyone have any suggestions as to what might be going on and what might be done to fix the problem?