When calling for heat on drivers side zone, passenger side zone blows air conditioning. Is this a sensor problem or mechanical problem?
air conditioning / heat zone controls on 1999 Buick Park Avenue
The fault you are describing with your 1999 Buick Park Avenue is most commonly caused by a failed temperature door actuator. I would classify that as a mechanical problem. I would recommend that you have the problem properly diagnosed before attempting any repairs. Please use the following link to find a shop near you http://repairpal.com/directory?address=37772&car_brand_names=Buick