they are broken. there is usually a little pipe where the air goes throughso tha could be dissconected too.
I'm not sure what vents you are talking about, but usually air vents are known to be working if there is air flowing through them.
The air is off.
Vacuum hose that runs over the thermostat housing is leaking at that location.
Jammed blend door or blockage in the ducts if you mean to say air isn't blowing through at all.
vacuum leak?
The air should be comming out of the defroster vents. If so, most likely, it is the vacuum line that controls the vents. It is on top of the engine below the air cleaner, and runs to the front right of the engine. Buy the replacment so you know what your are looking for.
replace? why not fix it?
There may be something blocking the deflectors from sending air up there.
How do you know it is charged properly? If you did not put gauges on the system? If no air is coming thru the vents the coil may be clogged. This list could take a long time!!
Warm(er) air rises - if vents were high up there would be little circulation without fans.
The blend door actuator may not be working.
check to see if the controls for the vents are working, there is ususally a vaccum control unit and it may mot be working on the rear vents. hope it helps. duboff