Cooling and Heatting

The air only blows out through the bottom vents and not the top vents, hot or cold. What causes this?

Usually when this happens (in practically all cases) the problem is the blend door does not move properly.

Due to the door being stuck, disconnected from the linkage or broken.

In some circumstances the blend door motor is at fault.

Most times, part of the dash must be removed to gain access to the ductwork.

Blend doors.
Cable, vacuum, or electric operated ? ( don’t know the bravada system, you didn’t state the year.)

If electric, they’re stuck in that position and may have stripped the motor. Find what’s in there causing them to hang up, replace motor.
May also be a switch.

If vacuum, a leak will allow them to spring back to a zero position. Fix vacuum leak, which could be anywhere from hoses in engine area to vacuum switches or push/pull diaphrams.

If cable oprerated, a sticking door can allow levers to break if forced, or a cable end is off.

If A.T.C. the plot thickens. ( automatic temp control )

By the way, it a 2003 Bravada

There’s nothing wrong with the blend door. The blend door is what provides the control for heat or cooling. The problem you describe is with the vent control doors. These are controlled by engine vacuum. When vacuum is lost to the system it will default to the defrost position. Since the air only comes out of the bottom vents it points to the vent control module manifold.


I stand corrected. The 2003 Bravada doesn’t use engine vacuum for the vent control doors. This systems vent control doors are controlled with electronic actuators. And what controls the positions of these vent control doors is the heating/ventilation/airconditioning control module.


AKA, look for a hose off somewhere. If any work has been done under the hood just before the onset of the condition …that would be where I’d look. An ultrasonic leak detector works well in this situation, but they’re rarely in anyone’s tool box.

Thank you. I see a lot of people on here call the air control doors blend doors. Blend doors are the doors that control air temperature, not air direction.