Yep I searched the heck out if this...
All I can find is info that doesn't match my '86
So...
'86 IROC, 305 TPI w AC
Short...
Where does the vacuum line controlling the diverter valve come from??? It's NOT the hvac controls!!!
Long...
Previous owner tapped the heater diverter valve vacuum straight to the manifold. As such it's always closed (I think) . Not a problem at the moment, but in a just a few weeks Colorado weather can be "brisk" in the am.
Anyway... I've tried to addresses ALL the vacuum leaks both under the hood and under the dash and I really don't want to leave a vacuum line open just because I can't find it!
I'm guessing the hard line is broken off inside one of my mutilated wiring harness bundles and I can't spot it under the dash. Of course I don't know what I'm looking for either.
My '86 only has ONE bundle of vacuum lines at the hvac control NOT two as the later cars have. And, no, I'm not missing one. It was never there.
Make sense?
Thanks in advance
Eric

 

Stock the line (thin, hard plastic) came out of the hvac harness. The ac control head switched vacuum on/off to it.

Your car has either had the control head swapped out for an earlier one (most likely) or has been otherwise fargled.

At this point if you've verified the vac switch does not exist on your particular control head I'd just remove the diverter valve. Early thirdgens didn't use them.

Another option is to find the correct control head. It will have to have the needed vac switch AND the AC ON rad fan switch.

 

Well that explains why the parts catalog doesn't actually list the valve for an '86.
So, how, exactly, does the heater valve in an 86 work?

 

Vacuum closes the valve and stops the flow of hot water thru the heater core. Under AC operations this reportedly results in slightly lower air temps.

I know the valve was installed on 87s and not on 85s.