98 Jimmy A/C Vent problem

Hello, My 1998 S15 GMC Jimmy SLS 4X4 has 128,000mi w/4.3L engine. When I turn A/C selector knob to far right for windshield defrost most of the air blows out the front dash vents regardless of fan speed. Also, with everything OFF air blows slightly out the front dash vents while cruising at highway speed. I checked the vacuum lines behind the dash which appear to be intact.

I removed bottom panels under dash and observed that none of the actuators move while turning the selector knob to any position. Appears to be no vacuum signal at the two closest to the gas pedal. Vacuum source line appears to be connected to the transfer case switch but hard to see. The temp knob works fine. Any help is greatly appreciated!

Vac actuator under the dash