maybe the vacuum actuators are not working to the fullest. or some linkage is cracked, its all plastic. pretty sure the pump on the pass side works the air flow, try moving the arm further one way or the other when its on vent to see if you can make it stop blowing out the defroster. dont push to hard or force it as it could break if not broken already. you can turn the car on, and then change the air flow and watch it move to get a idea of how it works, and what it moves.
pic from this thread. http://www.grandprixforums.net/blend...ent-21941.html its how to change the blend door actuators, but it also shows the vacuum pumps for air flow. you go the same way to get to them as the actuators.
its the round part in the lower right corner of the pic. the round part could be bad, or the linkage broke, or a vac line cracked maybe. the pass side you only have to take the glove box off, and look hard to the left to see this part, its close to the dash face.
