air conditioner

there is a vaccum leak at the check valve for the inside controls. it is a little round cannister that is a one way check valve so the doors do not change on accelaration. Roy

This sounds like an airflow issue. The A/C vents are controlled by a system that runs of engine vacuum. When there is a vacuum leak in the system this is the exact symptom you'll experience. I would have a shop check for vacuum leaks in the climate control system: http://repairpal.com/chevrolet-repair-in-rustburg-virginia