[clipity]

I had the same problem with my 89 burb.The problem with mine was the heater cable had come undone from the lever that controls the flap.If you open the glovebox you can get to it. You can remove the box or with mine I just pulled the door down.On top of the heater box you should be able to see the lever if the cable is still on it might be at the lever on the dash side.

Hope this helps Derreck.