Just wondering if anyone has an actual diagram of an '86 K5 Blazer heater box (w AC) or has experienced this problem firsthand in the past. Trying to get my heater to work. All I have is 'vent' and it won't switch to heat or defrost. (March in Illinois... MUST have defrost)! Have good vacuum going to the temp control, I can hear that tiny 'hiss' when I switch the settings. I do hear a door closing somewhere in the system but apparently not whichever one switches the air direction. Seems like I may have a stuck door or a bad vacuum actuator? Just wondering which one to try to find / get access to. Would save me some hit-or-miss if anyone actually knows which one / where it is. Thanks in advance for any help!
I lost my defrost as well, in my case it was the switch assembly that went bad. It's an electric/vacuum hybrid as you might've guessed and part of mine wore out. Not sure if you're having the exact same problems as I was, but it was just a though.
Well I guess I don't need that anymore. Dug into it last night and found some bellcrank type lever that was flipped backwards... no idea how that happened (previous owner?) But it all works now. Very relieved to NOT have to pull that heater box! Never did find an actual diagram but if I do I will attach it here in case it helps anyone with a future search. Thanks again!