cool air out of the left center vent warm comes out right center vent

When using the air conditioning, cooled air comes out of the left center vent and warm air comes out of the right center vent. I have tried all combinations of the air conditioning buttons in an attempt to get cool air out of the left vents, but have had no luck. Is there some sort of valve inside the system that isn't actuating to allow cooled air to these vents ?