GM / General Motors: 95 Sonoma PU Heater/AC

I have a 95 Sonoma PU with 4.3 l v-6, both heater and A/C.

Everything was working fine. Now the "air door" that switches from "floor
air flow" to upper dash vents no longer works.
ALL air flow in out the bottom vents, A/C, outside vent and of course heat.

This PU has lots of relays under the hood next to the heater, A/C housing
and some in the glove box, could one of them be bad?

I have checked fuses and all are okay..

Help, suggestions Please?