When running the A/C on my Buick Lesabre, cold air only comes out of the passenger side of the dash vents. Warm air comes out of the drivers side. The car does NOT have the dual control climate system. It seems something may be blocked under the dash, keeping the cold air to the right side of the car. Any ideas?

The most common cause in these cars is low refrigerant charge (R134A refrigerant). The safest and proper way is to have the system leak tested and the AC pressures tested with gauges. That said many people buy the precharged cans of refrigerant that come with a charging hose and low side (this is the side refrigerant is added to) charge indicator for about $20. These cans also contain oil for the A/C system. Don't overcharge the system.

Note if you have a leak it will quit again. How long it'll last depends on the nature and severity of the leak.

You may have a bad mode door actuator and you should check the freon in the system if the freon was low it could cause this particular problem.