trinitydigital

I have a 1988 coupe and would be greatful for some insight. It appears through diagram, that the c4 has 2 vacuum sorces from the firewall. 1.) is uder the brake booster but I can't pinpoint the other one. It seems to be under the wiper motor on diagram but I can't find it on my car. Also, it seems to have a check valve before the firewall from that same vaccuum source when I look at the diagrams. ANY SPECIFIC HELP?

trinitydigital

Anyone have some insight?

AGENT 86

The check valve is at the back of motor, it tees off to cruise/vacuum tank and the other line goes to HVAC via the big wire harness in center of firewall.

Square

Is this the little plastic cylinder with a cone shaped top leading to one hose connection and 2 hose connections on the bottom in a "L" configuration?

If that is the item, then I have a photo showing it that I can email to you.

trinitydigital

I.m not clear on HVAC, the harness you name or the check valve. Can anyone shed more light on this? It sounds like you are getting close to my problem now.

trinitydigital

I know I'm close now. Can you shed more light on this? Diagram, photos?, Page number in Service manual?

AGENT 86

Maybe if you explained what your problem is, we might be able to shed some light on it.

trinitydigital

Thanks AGENT 86. The problem is that the AC is weak, After inspecting the vaccuum lines acurately, I see that the secondary vaccum source( wherever it is) is bypassed and there is no check valve I can see according to all the diagrams I've come up with including the Service manual. It's basically been drastically messed with by so called techs and I'm desperately looking for help during this monster of a Texas summer. I can't find the vaccuum source in the back of the firewall.

trinitydigital

You wrote"The check valve is at the back of motor, it tees off to cruise/vacuum tank and the other line goes to HVAC via the big wire harness in center of firewall."Can you be more speific as to where exactly?

AGENT 86

My pics are a nightmare since transferring to my new computer. I'll look again in the morning. The tee and check valve are beside distributor,towards drivers side valve cover.
There is only one vacuum source for HVAC (excluding the vacuum storage tank) and it comes from the port on pass side of plenum.

JamesRS

Here is the check valve that Agent 86 is referring to.

http://www.ecklers.com/product.asp?p...8&dept_id=1183

This valve will allow the engine to build up and hold vacuum in the vacuum canister to control the heater and A/C vents as well as the cruise control. Without it, the vents won't work properly.

trinitydigital

The specific problem I have is locating the vaccum line from the firewall to the check valve. The vaccum line from the plenum now goes straight to the vaccum tank with no check valve. That's what the so called tech has done.

trinitydigital

the other line goes to HVAC via the big wire harness in center of firewall."Can you be more speific as to where exactly?

JamesRS

This is how the routing goes on my 84. The line goes from the plenum to the check valve, splits on the back side of the check valve, one side goes to the HVAC control through the plastic vacuum line in the harness and the other connects to a rubber vacuum line that goes to the vacuum tank. Halfway down the path to the vacuum tank on the drivers side inner fender there is a "T" connector where the vacuum line splits off and runs to the cruise control. There is a second line coming out of the cruise control that runs into the firewall under the brake master cylindar. I believe that is how the internal A/C ducts get their vacuum.

93*Corvette

Can this picture help this guy. This is from my 93... It the valve under the fuel rail.... Don't know if the 80's are the same.... Mine is also a LT1, so it's probably not the same.

AGENT 86

That second line goes to the brake switch, used for cruise only. The HVAC gets vacuum from the line that goes into wire harness.

AGENT 86

Still can't find my pic showing where the vac line enters wire harness.
Here is a pic showing the check valve and it's tee. I'll keep looking for the other pic.
The harness that has the vac line, enters the firewall near the pass valve cover. Behind the distributor, is where the vac line enters the harness.

trinitydigital

"The HVAC gets vacuum from the line that goes into wire harness."

That's the one I can't locate. Where does the HVAC sit? Maybe I can trace it back.

trinitydigital

My AC vaccum setup is missing some lines. Even w/ diagram from service manual it's tough to see where these attach, I found the Connector ASM vacuum hose. It's missing One black line going in and one going out. Man this is tough. Ican't even see where this Connector ASM vacuum hose connects. It's just floating in the diagram and hanging under the passenger hush panel. I can't believe these so called techs who are trusted to fix things and just make them worse.

JamesRS

Thanks Agent 86, I didn't know that.

After seeing the pictures posted by 93*Corvette I'm going to stop becaust the 84 vacuum lines and check valve look completely different and I wouldn't want to misdirect you trinity digital.