Air only blows out defrost vents - Bonneville Pontiac Cars & Trucks

SOURCE: air will not blow out of panel vents

vents are blocked so air is diverted to other vents, check and clean if necessary

SOURCE: Heat wont blow through heater or defroster vents

common problem, check under dash by the gas pedal if control arms are muving went selecting from ac to heat cuz this it is the control for the vents to go from ac to heat and to defrost.

SOURCE: PROBLEM WHEN SELECTING THE DIRECTION FOR THE AIR

Sounds like you have a supply vacuum problem. When you lose supply vacuum to the control head it defaults to defrost.

SOURCE: climate control system only blow air out defrost vent

there is a good chance that you blend air door is stuck closed over your heater core and therefore not allowing the heat to flow, also your door that opens and close your direction of flow from the floor ,das,vent and defrost.your going to have to remove the lower cowling of the dash on the passenger side analso some of the center dash to actually check to see if the cable,servo motors. are acuating the doors.the issue could be just a stuck door or a misaligned cable or that it came off. that falls under the mechanical side of probabilities. electrical would most likely be a faulty selector switch or a servo motor

SOURCE: All Air Conditioning blows our the defrost vents

Some thing you could look at would be this. The control is usually fed by a vacuum line or small hose thats is connected to your intake manifold.
With a cold engine,look for a skinny vacuum hose that runs from the intake toward the fire wall . It should be going inside the cab and connecting to the A/C vent control.Some times the hose becomes disconnected or splits or cracks due to heat under the hood.
Thats usually the trouble.
I hope this helps you.