It's 105 degrees outside today and only June 6th...yay! I turned the AC on my 98 Blazer and hit the recirculate button. I didn't hear any change in the pitch of the blower, so whenever I got home I looked behind the glove box and the door was open. I shut the AC off and hit the recirculate and it closed. As soon as I turned the AC back on I noticed it immediately opened even with the light still on the recirc button. (Setting was panel vent only, max cold on temp control, AC and Recirculate on. Honestly I've never used the 'Auto' function.) Is it supposed to operate like that or is there a different door closing that I'm not aware of? If this isn't working like it should, I'll do an HVAC reset.

 

Have you ever replaced your under-hood vacuum hoses? If you have a leak in them, it could be affecting the actuators for your HVAC system. I have a link in my signature from when I did it for my 99 LT. Mine has the 4-button transfercase.

 

After looking at the fuse panel I noticed something odd-there wasn't any 20A fuse in the HVAC slot. All of my functions seem to work without it so I'm puzzled what's going on, unless a PO did some wiring that bypassed the fuse.