Ok I am officially stumped. I’ve looked at many vacuum diagrams for this car (79) and I don’t understand where/why this line is on the passenger side. From all the videos I’ve watched no vacuum lines come over here? The hose with the red X is apparently from the water pump/heater core that was bypassed. Why is that attached to this check valve? Also why do I have an open line with no hose? (Circled in photo). Where does this go? Does it need to be capped off? The one hose at the check valve connects to the T in the second photo. The headlights will close when the car is running but do not go up unless put up manually.

All of my other vacuum lines seem to be tight and the lights wouldn’t close unless I had at least some vacuum. I do have a vacuum gauge coming in, is there anything else to try in the meantime?? (The override valve under the steering column is closed)

 

THe first picture is your temperature control valve. A vac line from your heater switch inside the car goes to that valve and if your heater control selector switch is open ( like hot/cold) there should be a vacuum to that valve. If is is not hooked up and the switch is pushed to the right you will get a vacuum leak.But the picture seems to shw a vacuum line already over there. I might suggest getting yourself a vacuum diagram of the car. There are lots of hoses and lots of places for leaks. And enough of those leaks will keep the car from running right. And again, it has nothing to do with your lights unless someone didn't know what it was for and pulled a vacuum off the light system. This switch opens and closes which lets hot water into the heater which controls the temp inside the car. .

 

Thanks for the info! My valve was open on the AC controls but unfortunately no dice. I have a suspicion i have to repair the actuators from some research, Ill give that a go tomorrow when the parts come in

 

It seems like you're looking for a magic bullet - aha here's the sole source of my problem. That could be, but be aware the whole system is likely compromised a bit that adds up to larger failure.

Here's what I would do: Start at the engine's vacuum source and cut off about 3/8"-1/2" of hose and reconnect it. Follow this hose to it's next connection and do the same. Follow every hose you have (in a systematic fashion) and clip the hose end. These hoses have been there a very long time and can develop cracks and a "set" on the fitting's barb. Clipping off the end will put a fresh section on the connection and will seal better. This will also locate a major disconnect or failure point, if it exists, just because you are examining every connection.

You may want to wait to do this until your vacuum gauge comes in, then you can do two things at the same time. Beginning at the block, measure vacuum from the manifold fitting — should be ~18"-22"hg. As you work down the lines and after you clip the end, use the gauge to see what the vacuum is. You shouldn't see much of any drop at all. If you do, then that segment needs to be inspected better.

At the vacuum tank - horizontal between the front wheels on a '79, measure the amount of vacuum at the tank's outlet(s). I'd stop here momentarily and do a "leak down" test on the tank. With only the engine vacuum source line and gauge on an outlet (any/all other outlets are capped- again I'm not familiar with the design of the later C3 tanks as I have an earlier configured system), get a reading with engine running and then shut the engine off to see how long it takes to lose vacuum.

Continue on all the way to the actuator cans on each headlight door.

 

On my 78 there is a vacuum source that foes into the cabin and the heater controls. From there the lever moves the control to whatever function you want, like heat. That allows the vacuum to go to the control valve at your 2 heater hoses. The vacuum opens the valve and lets hot water into the heater. It sounds like you have a lot of putting back together stuff on the car. As Mr.67;72 suggests, get a plan and work your way thru it slowly. Don't go buying a lot of parts until you know they are needed. The heater control in the car, for example sometimes only needs to be cleaned up and a little lubricant on the hose ends to get it to seal back up rather than buying all new parts. The valve at the heater hoses however cannot be fixed if it doesn't move when vacuum is supplied so for that you need new. When you get to the actuator cans and all of those hoses it really isn't difficult to figure out how the up and down thing works. But you really need a diagram or book. Or you can throw out all those hoses and just put electric motors in, like a lot of us that aren't concerned with originality do. While you are there you might as well do an LS swap.....Welcome to the Corvette slippery slope.

 

Unless I'm not seeing it clearly in your first picture, you have a nipple on the heater control valve with nothing attached to it AND you have a hose sitting there that should be attached to the nipple.

 

there are 2 nipples there the one coming out is already attached, i don’t know why the other is open/where it’s supposed to go

 

1979 Corvette heater control valve should have only one hose, look at them online

 

very interesting, I took the hose off and it’s blocked off, put it on the other side. No change with the vacuum system. Wonder if they just capped it to leave the option open to add back whatever they removed

 

Have you considered they installed the wrong valve?

 

if the valve does hold vacuum, closes water off, it is good.
leaks, bad

weird with 2 nipples, one looks like a plug so no foul.

 

alright so I got my gauge in, I have vacuum all the way up to the tank. I have ~15-20 at the hoses going into the tank, however when removed I have absolutely nothing in the tank itself. The lights will close very sluggishly but they won’t open. So there has to be vacuum at the actuators, so I’m confused about the tank itself, it seems solid so maybe the leak at the actuators is big enough to not even allow the tank to build vacuum? I removed the rubber boot dust cover thing on the actuator and there’s a pretty decent size rip in the actuator, so I plan to replace those parts when they come in and cross my fingers that’s my solution. I tried pumping up the actuator and bypassing the tank and still no dice. Part should be in on Tuesday! Let me know if anything here sounds wrong!!

 

Those boots that fit tight to the stems in the actuators (not the accordion dust boots) do need to be undamaged - pic below. If these are what you ordered, make sure to put some light grease on the stem and the pie plate's flange to help slide the boot on and seal it. I'm sure they will help (and maybe solve your issue if nothing else is wrong). Be forewarned that with the pie-plate activators, you need to pump the hand-held vac at least 60-75 times to begin registering - ever seen Popeye and his forearms? When he wasn't brawling with Bluto or wooing Olive Oyl, his side job was in St. Louis to test these actuators!

I believe the stem seals, if ripped, could be enough to compromise the tank's ability to hold vacuum. To be sure, plug one of the tank's nipples that go to a headlight relay, hook the other nipple that goes to the other relay to your vac gauge. Start the engine and see how long the tank will maintain the vacuum on the gauge. If the vac hoses to the tank are good with good connections, the tank should hold well. Some folks report 24 hours, but I'd be thrilled with 1 or 2. (Have you checked the one-way valve by the engine's vac fitting? That's the small disk with a single port on one side and two on the other. If it's not functioning correctly your tank won't hold any vacuum.)

 

This was the problem! Unfortunately the link on one of them was seized and I broke it in the process of trying to take it off, however, that boot was completely destroyed. I put the other one back in just fine and plugged the open holes with my fingers on the busted side and it went up and down no problem! Bummed the other broke but at least I know that was my issue. It must have been leaking air out of that broken seal so fast that the tank couldnt create vacuum at all. Thank you for the help!! I am sure youll see me post on something else, lol