Hello Fellow C3'rs,
Working on the interior ventilation vacuum controls of my 1980 and would love to hear from others who have addressed these issues on their cars.

My car is mostly stock (and fairly neglected) 1980 - L48, 4 speed, with A/C. The emissions vacuum lines were a mess (hacked by previous owner). Lines inside the cabin appear to be original, unmolested, and surprisingly "healthy". FYI: I've successfully rebuilt my headlight vacuum systems so familiar with principles. I also just followed the blower motor upgrade posts to complete that task. Unable to find past posts with details on a later C3 controls. Lots of posts declaring how hard it is to rebuild the dash has me trying to avoid that process.

So far I've removed the glove box allowing me to see where lines pass from the firewall to the cabin, and the water shutoff valve. Pulled the side of the center console for access to the control switch, and removed the center instrument to see even more of the lines. All of the hoses appear to be original and healthy (Soft and flexible but not squishy. No cracks, no chalking, no other visible problems). All of the vent doors and flaps will move with reasonable force and typical air actuator sounds accompany those movements.

Issues:
#1 - My source line was cut on the firewall side (thanks previous owner). All the diagrams simply label one line as "source" without details of where it connects. I added a T to my headlight source thinking manifold vacuum is likely correct. Can anyone confirm the proper location for the HVAC controls to tie into the engine vacuum system?

#2 - When using my hand pump to manually pull a vacuum on the HVAC system at the firewall (sucking on the line that was cut), a sealed vacuum is never achieved. It's not wide open flow, but no actual vacuum. Should the controls system achieve a true vacuum (like the headlight switch system)? I have not disassembled the dash, but I can see at least 70-80% of the lines. However, the diagrams indicate two T connecters exist, and I have not seen either of those. Curious where other people have found their failures?

#3 - The manually activated lever tab that is supposed to press the plunger on the water shutoff valve is not at all close to the plunger (see pict). Based on the dust layer, the PO didn't hack this up (appears original). Looking at aftermarket cartoon diagrams, there appears to be a "plunger button" on the end of the valve. I'm wondering if mine fell/broke off long ago? I can make something that will work, but would appreciate knowing what correct is if anyone knows.

#4 - The control rebuild kit I bought (Dr Rebuild) uses the typical large OD rubber lines. All of the HVAC lines in my car are smaller ID/OD (still correctly color coded). I haven't found a source for an exact match to my lines. Got something that will work from Amazon, but it's a little thinner wall, and slightly smaller OD. Any know of a true match, or a better kit?

I've been reluctant to start cutting lines which look healthy to test individual vacuum circuits. Hopefully someone fought this battle and has advice on which items are most likely to fail.


Vacuum diagram from Assembly Manual - Only lists "source", also shows "button" on WSV?


Rebuild kit diagram - also lists "source" without showing location, and shows a "button" on the WSV.


My WSV with a 1/4 inch gap between the lever and the plunger.

Truly appreciate anyone with experience and knowledge on this subject to share.

 

My guess is you still have a leak. I would start at your "source", and see what you pull for vacuum there.

If you have decent vacuum to begin with, you should be able to find where the drop is. If you can procure a few sets of hemostats, its a lot easier to temporarily crimp the lines, as opposed to removing and plugging.

 

1977-1982 HVAC is all the same...Only change I know of is a newer style HWSVS (Hot Water Shutoff Vacuum Switch)
1. Your source line is any line that is full manifold vacuum. The original source line "T" after the check valve small hose side.
2a. Me, First I would pull a vacuum at each actuator just to rule out a bad one.
2b. There are 2 "T", one on the engine side before grommet (source line) and the other "T" feeds the HVAC vacuum switch (Port 1 A/C car) and the Hot Water Shutoff Vacuum Switch...
2c. Trying to pull and hold a vacuum from the source line is hit or miss. If you have ever taken one of these vacuum switches apart it is a real maze in there.
3a. The reason you don't see a button on the HWSVS is because your 1980 has a newer style vacuum switch then the one shown on your photo. Your OK there... But do post a larger photo of the vacuum lines there, to me something MAY be askew?
3b. You have some real bubba going on with that spring, I have no idea whats going on there. There should be a turn buckle on the cable for some adjustment. If you have a little round magnet about 1/4" thick try putting that on the flat tab that pushes the button in...
4a. Use the kit you already purchased...It has vacuum rated hoses and should have came with some 1/4" spring clamps, use them where you can. Purchase more if needed...
4b. When installing the new vacuum lines make sure (Port 2 gets blocked capped A/C car and port 5 Non A/C car), if you look at your original vacuum manifold (If A/C car) port 2 is blocked...
Here is a diagram of the vacuum switch and what actuators it supply's. A/C control ports Left Non A/C control ports Right...

 

The spring is Bubba mod unless that is a new addition for 1980 but what purpose would it serve since the wire "cable" isn't spring loaded in operation. Maybe Bubba had a problem and decided to mask it with the spring? That vacuum switch is a new design for 1980 and I'm unfamiliar with it. But the 1980+ switch has screw holes and your switch has a plastic zip tie holding it?

 

I'd like to give credit to whomever created this pic but I don't remeber where/who I got it. Regardless, It shows some of the hot water switch capillary tubing routing and the switch port detail. NOTE: this switch is the 1977-79 design with actual plunger as depicted in your drawing.

 

This shows the intake manifold vacuum "tee" which is the source of vacuum. From there it goes through a filter and a check valve then to the fatter vacuum hose through a white plastic tee which splits off one side to the skinny capillary line that goes back into the cabin through a rubber grommet. Ignore the fatter hosing near the firewall which I have X'd out. Thee capillary tube is obscured in this photo so you don't see it going through the firewall. It comes out inside the cabin and can been seen if the glovebox liner is removed.

 

A tip on some threads dealing with diagnosing the wiper door / hidden headlight vacuum system suggested:

Purchase a cheap HVAC (or other) vacuum pump and 25' of hose. Put it outside your garage or workspace where you don't hear it.

Use it as a source for your troubleshooting.

You'll be able to HEAR where vacuum is leaking.

Are all these switches / valves / actuators supposed to completely SEAL off vacuum --- or as the seals age, leak a little bit, with manifold vacuum simply overpowering the leaks.

I don't know the answer to that.

On a '68 or early '69 there are two or three sources of vacuum that penetrate the firewall.

The two feeding the ww door and headlight controls are Y'd in the engine bay on early models (3), T'd under the dash on later. (2)

Vacuum for the HVAC controls penetrates the firewall over on the passenger side, coming off an unusual "T" --- two fat one small ports.

I can't say how consistent this is with a 1980, sorry.

 

First, thank you all for the helpful feedback (love this forum)!
Must admit I originally thought the situation was weak 80's design/build quality. Popped one end of Bubba's spring off and the whole situation makes more sense.

dunny - I agree, there is at least one leak (probably a few). I haven't measured my vacuum recently, but its usually 11-13. I'll verify it's still healthy next time I start it up. I also REALLY like your crimping segments suggestion. Great way to take smaller diagnosing bites.

bmotojoe - Somehow I failed to think of using my hand pump to check individual actuators (learned that working on the headlights - old man memory). Knowing my valve version is a newer style is comforting. After removing Bubba's spring and zip tie (which was holding the three line vacuum line "connector"), I pulled the connector off the valve to see if it seemed healthy and it does. It also matches the one shown in the second image 70s provided. Then I found the turnbuckle you mentioned and was able to reduce the lever to plunger gap (Very helpful!). Used your temporary magnet trick and the lever now depresses the plunger. A little concerned because the whole front face presses in a little with the plunger but it might still be functional (pict below). My selector looks like the dirty version in your image and I had already verified it's plumbed to match the diagrams (pict below). Also appreciate your thoughts on replacing the lines with the clips provided. Thank you thank you thank you!!

70s - Now that I've removed the spring and the zip-tie, and gained an understanding of the adjuster, you are correct. The spring was someone's hack to cover an issue. Confident I'll get it adjusted with all my new knowledge.
What is the large black item on the HWSVS in your first image? Seems unnecessarily large to be a cap. The three line connector appears to use that port for orientation leaving it open for exhaust/vent. However, I see the port labels on the old style version has the opposite orientation. My paper diagrams all match the tags on the older style but they also all cover multiple years. Should be easy to test and verify.
Happy to see my configuration is very similar to your marked up engine image. Truly appreciate all of your information and suggestions.

wadenelson - Pretty sure I read the same thread suggesting a vacuum pump and it's a solid option that I've considered. They start at $100 which isn't horrible, but I won't use it often enough to dedicate the storage space. After successfully rebuilding my headlight system without one, I decided to put some effort into this before I buy another tool. I do appreciate the thoughts and the info though!


After de-Bubbafication with temporary magnet in place


My selector valve



Too hot to really progress tonight and my pesky job makes me work mornings, but I will get back into this soon.
One last time, thank you ALL!!!

 

Here are a couple more photos to keep in your memory bank...
Photo 1 is how I test these HVAC vacuum function switches.
On a A/C car I block or cap port 2.
Land your vacuum source line on port 1.
With the vacuum switch lever arm in the full vertical position you should be able to pull and hold a vacuum...
If not your vacuum switch is either faulty or you could try opening it up and re-greasing the maze with a proven vacuum grease.
Anytime you move the lever arm past vertical you are either exhausting vacuum or sending vacuum to the actuator(s)
And then anytime you move the lever arm to another position the previous actuator(s) needs to exhaust, this is done through the switch itself. That's why it is difficult to test the system by pulling a vacuum from the source line when it's still attached to the control assembly....
Photo 2 shows a breakdown of your HWSVS and how to test if it holds a vacuum...
You said you see the end of the switch moving in when the button is pressed, that is just the shape of the spool and is totally normal...

 

That be me...

 

UPDATE: I've had a chance to test the HWSVS with my hand vacuum pump and it will not hold any sort of vacuum. With several quick pumps it will achieve some negative pressure (-12/14 inHg), but it drops to 0 in less than 2 seconds. Couldn't find any new 1980 style units on the major suppliers sites. I'll be trying to refurb it (gotta find the grease from bmotojoe's response). If that doesn't work, I may buy the older style.
Tested the actuator down in the passenger footwell, and in a similar way, quick pumps will temporarily achieve negative pressure, but it bleeds off in about two seconds. The flap will move slowly IF its pumped enough to sustain -20 inHG, but it will not return when pressure is released. Cleaning and lubricating the pivot points may help lower the force required, but it won't make up for the leaking actuator.
Tested the fresh air actuator and no pressure, no movement. This one appears to be a tough one to replace. I'll search for tips or tricks in the forum, but may just figure out a way to lock it in the closed position (to reduce hot engine air intake).
Research: I was fairly surprised at the prices for new actuators on the vette vendors sites ($55-60 each). In anyone knows the original GM part numbers, please pass them on.
For now I'll have to block the vacuum and put it back together without repairs. Inspection is due and it will take some time for me to get back on it.
Appreciate everything you all put into responding. Your time and knowledge is valuable and I'm so happy you shared both.

 

I hope forum member interpon responds to your last post as he has a good writ-up on the plenum actuator and a problem we both found with those actuators hoses...
Here are some part numbers:
HWSVS GM #14009284
Recalculation Actuator GM #1996608 & Superseded to GM #1996505
Plenum Actuator GM #1996607
Plenum Actuator Hose GM #3984652
80-82 Heater Air Distribution Actuator GM #1996595

 

these threads?
https://www.corvetteforum.com/forums...-switch-2.html

or

https://www.corvetteforum.com/forums...cuum-line.html

 

Yep, your 2nd link...
Actually, both links are helpful...