I have a 94 ST Blazer 4x4. The AC and Heat both work fine but they will only blow air out of the defrost vents and the bottom vents on the floor. No matter what I select on the control panel it always comes out of these two areas. Any ideas on how to get the air to come out of my main level vents? Thanks.

I have a 94 ST Blazer 4x4. The AC and Heat both work fine but they will only blow air out of the defrost vents and the bottom vents on the floor. No matter what I select on the control panel it always comes out of these two areas. Any ideas on how to get the air to come out of my main level vents? Thanks.

Check the vacum port on the rear of the intake..right rear side near the distibutor.
This port supplies the vacum for your outlet doors and if there is a leak, the doors will default.