hi, i am banging my head against the wall on this one. i have an '87 firebird V6 2.8, no cruise, no A/c, manual transmission. Since i bought the car last year....on the back on the intake plenum there is a vacuum T inlet, the driver's side hose goes to the brake booster. But the right side which is supposed to go to some hvac hardline is missing. where do i find the location of the hvac hard line coming out of the firewall?? I have taken the plastic off the wiring harness and just wires, no vacuum lines. I have searched for hours. from research i've done there is supposed to be a cone shaped check valve that 'T's off to cruise and then to hvac. I have no loose lines anywhere. Please help, maybe take a pic of yours to show me what i'm missing? ( if i submitted to the wrong forum let me know)

i put a vacuum line and capped it for now

i removed the sheath from the harness but no vacuum lines

 

Probably goes to the vacuum reservoir and/or check valve. Butt since it's a 6-cyl, I haven't the vaguest dimmest foggiest remotest hint of a whiff of a glimpse of a clue how ANYTHING is arranged under the hood, since I've only ever seen one such that I'm willing to admit to myself to, and that was in a junkyard, and I averted my eyes within less than a second so as not to be ... tainted. Such that it's supposed to feed the HVAC system and maintain vacuum when that goes away during attempts at acceleration (largely futile no doubt), specifically, the vacuum motors that control where the air comes out in the cabin, and the cruise control. Although, being a 6-cyl POS low-option car, might not have cruise control, so that simplifies things a bit. Might explain why your HVAC blower only blows as if in the Defrost mode. Don't ask how I already know that that's what it does.