Ac not blowing through center vents - Vehicle Parts & Accessories

sounds like vacumm modules in dash

Cornelius, vent problem could be a pinched or loose vacuum line on controller,faulty AC vacuum motor, faulty AC programmer,etc. needs to be checked out by a good Tech, diagnosed and estimate on repair.
As far as vehicle only blowing cool air, issue could be blend door issue, plugged AC condenser core dirt/debris, low AC refrigerant, plugged AC lines internal, failing compressor, etc., again should be checked out, diagnosed and estimate for repair by a good Tech.
Check the attached links,instruction and guides, Good luck
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1998 Buick Lesabre No Air From Dash Vents
http://repairpal.com/ac-vent-problem-346
Car AC Not Blowing Cold Enough Car Repair Information From MasterTechMark
My Car Is Not Cold What Could be Wrong Elite Auto Repair

My ac is only blowing on the defrost but none on the center dash vents. How do I clean the ac hoses? It may be blocked.

add freon and test

Bring the vehicle to a repair shop. This could be a dash board nightmare and you have to discon the SRS system before working on the vehicle.
Or its the position switch or its actuators. It a little tricky to remove the switch to see what happens once you do that and jump the terminals. The relay is pretty easy to check out with a voltmeter. Its your call the actuators are a pain to get to.

this problem is caused by a defective air temperature control blend door actuator motor, it is about center of dadsh in air ducting, it moves the door that diverts air for cold from ac or hot from heater, you must remove the dash to repace it, about a 15 hour job fotr a home mechanic with a factory repair manual, nearly imposs without one.

Vacuum line has to be connected to this system in order for it to work properly.

climate unit is bad

hello,good day,seems your recirculating pump need tobe check,ty

it sounds like a vacuume motor that is out or going out also check all vacuume lines for cracks