Auto Air Conditioning & Heater Repair: 2003 Jeep Grand cherokee A/C, 4.0L, 6Cyl, jeep grand cherokee, floor vents

Question
When we run our air conditioner in our vehicle, we receive cold air through our defrost vents and sometimes through our floor vents.  However, the main "body" vents do not blow any air through them.  One person told me it could be a "flapper" ?  I am not a mechanic but would like to know what I could do to try and fix this so our main vents start blowing out air again.

Answer
Greg,
Inside your ducting in the dash, there are several doors "flappers" as this person described them as, that open and close sending the air to wherever you want to as set by the control head.
There are two systems that car manufacturers use to operate these doors. I am unsure of which type your truck uses.
The first is a vaccuum type system in which the control head sends electrical systems to a vaccuum control manifold. This vaccuum control manifold then translates these signals into vaccuum being pulled on a series of vaccuum lines. These lines lead to the door actuators themselves and open the appropriate ones. If this is the type of system your Jeep uses, then it could be several things. A dry-rotted vaccuum line may be losing some of its vaccuum through a crack or pinhole, or it may be the connection at the actuator itself or at the VCM is loose and losing its vaccum from there. Or it may even be that your vaccuum control manifold is going bad. The diaghrams inside it may be worn out.
If you have the all electrical system, that would lead me to zero in on the actuator or motor itself weakening and closing as the high speed air passes over it.
Either way, I highly recommend you taking this to a reputable A/C shop or even the dealer to troubleshoot. It is a fairly in-depth process finding a fault inthese systems, the largest part being the disassembly of the dash panels and ductworking. They should also have the appropriate diagnostic equipment that would make this job much easier and quicker than one person in his garage.
Thank you for the question, and I hope that I was able to help you out just a bit. If I can be of any more assistance now or in the future pleaselet me know.