Astro Van, AWD, '98, 85,000 miles, 6cyl, HVAC Problem

No air flow from front HVAC vents. Blower motor is running, and changes speed with the control. Had the same problem @ 60,000 miles(2 years ago). Took it to Chevy dealer and had it repaired. They unfortunatly caused other problems. Don't want to take it back to them. My guess is a vacum hose or electrical connection under the dash not allowing diverter flaps in the ductwork to operate. Note: vehicle has front and rear Heat and AC, rear HVAC
working fine. Anay ideas? Should I buy the repair manual and try to fix it or take it to another Chevy dealer?