heat vents not working

[BA.TA]

My heat and a/c only blow out of the defrost and floor vents no matter where the dial is set to on my 96 t/a. Anyone ever have this issue before? Are there any switches or plus that i should check out? Im not really sure what to look for.. Thanks.

[fleetmgr]

All the heater box doors are controlled by vacuum, so you may have a leak. Check the hose coming off the back of the intake, if it's ok then check all the plastic fittings along the way going to the dash selector, which is actually a valve. Then it goes to the actual vacuum motors on the doors inside the heater box.

[2001NBMZ28]

http://shbox.com/1/4th_gen_tech2.html#HVAC_vacuum