Ac starts blowing out defrost on its own

[black07sierra]

2007 NBS Sierra. Has the auto climate control. I'll be driving down the road and it switches from vent to defrost and I can't get it to switch back unless I stop and turn truck off. I guess it resets itself and then works fine. But it'll do it again in a day or two. I'm guessing the actuator is going bad. Anyone have an idea which actuator it is? I can see the one for recirculate and fresh air, I see the heat AC door actuator. There is one on very bottom of unit right above transmission hump in floor. I know the dash will most likely have to come out to fix it. Just need to know which actuator it is so I change the right one.

---------- Post added at 07:19 PM ---------- Previous post was at 05:22 PM ----------

I think I found it. I believe it's number 20 right?

http://www.trademotion.com/parts/200...gramCallOut=20

[black07sierra]

Mode actuator is answer. Default mode is defrost so you can drive it in winter if it fails.

[dipstick]

Try this first . Under the hood pull hvac/erac fuse. Wait 30 seconds put back.
Start truck ..but do touch any ac or heat controls for 1 minute if this is the problem should set it back to factory default.
Be good to go. If not will be the actuator at hump under dash.