'98 Olds LSS HVAC

I posted here about the problem with my father's LSS's vents a while back, but since I've recently (sadly) inherited the car I figured I'd start over.
'98 Olds LSS 3800 N/A.Yesterday was the first day it's even been fired up this year. Anyway, the HVAC system needs attention. All I get is heat from the floor and defrost vents, nothing from the dash vents, even on a warm day with the temp set to auto. Even with the fan turned off all I can feel is heat radiating from those vents and again, nothing from the dash vents regardless of the setting. If memory serves last year we could get A/C out of everything but the dash vents but now, only heat. Where should I start troubleshooting this thing? I really should get a service manual for this thing...
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Sorry to tell you but you are going to need more that a service manual if you are not a GM Tech. The problem it is at your blend doors, and that could be a number of things including but no limited to vaccumm, electrical and even a door stuck or broken, Good luck Oh I forgot the dash will have to come out sorry.

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