I am in the middle of putting in some different HVAC controls in my 'bird and have a question/need confirmation about the vacuum part of the controls. I have a diagram of the colored lines and know what they go to but, there is an extra grey vacuum line (circled in pic. below) not shown in the diagram.
It is Y'd into the main vacuum line (from the engine) and is on a seperate valve on the original HVAC controls. It only opens (or closes ?) when the temperature selecter is moved to full cold.
I am assuming this grey line is what operates the heater control valve.. is this a correct assumption ? Any help is appreciated.

 

That does in fact go to the heat control valve.

If your car doesn't have one, you can just cut the purple line off right by the "Y" and plug it, and just leave the grey one alone.

Or, you could add a heat control valve, and your A/C will work a little bit better in the summer time, since the heater core won't have hot water circulating in it all the time.

 

Thank you much RB.
My car does have a heater control valve but, no functioning A/C (for now anyways). Unfortunatly, the new controls have no provision for the h.c.v. as they came from a Corsica and the temp selector is out of a 95ish camaro.
Thanks again

 

To RB83L69: I have a 84Z28 without a heater control valve. Would it help my ac more in the summer? I do have constant warm air coming in all the time.

 

I think it might; I needed a control head & wiring harness and ended up with one with the vacuum setup like the one in the pic. So I added one to my 83, it does seem to keep the pass cabin a bit cooler, no warm air in the vents. I don't recall whether the valve needs to be normally open or normally closed though, but it isn't too hard to figure that out; I just used a HCV that's in-line, I looked through the catalog until I found one with the hose fitting orientation I wanted, that was the right size, and the right logic.

 

My ac does work much better when I bypass the heater so I am of the assumption that it would help my situation. It seems when I installed a valve in line of the heater and try to switch it off, it still lets some air thru. I was recommended to turn the valve completly backwards. I did and it works much better because of the backward pressure on the valve. Only trouble is that you have to open the hood each time you want to make a change . I had thought of puttting two electrically operated selinoids on the two lines. Maybe adding the hcv would do the trick for me.