Each vehicle will have simular systems to control the air vents in your car or truck. They are usually either electrically controlled, ot vacuum controlled motors that control air doors to direct air flow to the selected ducts in the cabin.
I find in a lot of vacuum systems, a leak, or disconnected hose between the vacuum tank and the control motors can cause the air doors to go to their spring loaded position. Usually defrost, or a combo of defrost and vent.
On the electrical controlled motor system, you will need to find out of the control motor itself has gone bad. In either case, there can be instructions that can aid in the trouble shooting of the system. But a blanket set of guide lines is not going to work for each type of car. If you post a specific model, yerar make and type of engine. Sedan and coupe 2 wheel and 4 wheel drive, allows me to look up your specific system and maybe allow me to help you diagnose your problem. But each one will be type specific.
Send emails to me, but include all of the details of the problem, and everything you have tried to fix it. You can email me and link me to a post and we can communicate so it may help others with the same problem, but email is the only wany I can send images you might need to trouble shoot.
Michael.D. Byers@delta. Com
Monday, August 14th, 2006 AT 2:58 PM