A/C Vaccume Problem (Please Help)
 

Car: 08/78 280zx N/A
Manual Air Condition

The problem started with my a/c vents only blowing on my feet. I took off the dash to investigate better and found that the actuators were not getting any vacuum pressure. So I began to remove all the vacuum lines from the one line coming in from the firewall to the vacuum tank, all the lines from the actuators to the a/c selector, and the vacuum lines from the manifold to the vacuum tank/valves. After I did this I tried it out, my passenger side was soaked, the heater control valve was leaking. Now I removed the heater control valve, and I am waiting for the part. I started the car today to check if I am getting any suction out of the two ports on the exhaust manifold, I pulled the line and put a thin paper in front of both ports and there was nothing. My cruise control doesn't not work, as well as my car takes two or three start-ups to get oil pressure for the car to run properly and I assume both are vacuum related issues. I have also replaced the oil pressure sender, but didn't help. Please help, its driving me crazy!

Welcome to ZDriver! :006:

DL a factory service manual at either XenonS130 - S130 Reference or XenonS30, depending on which model you actually have there. Manual may have some inspection and troubleshooting pages for you. Check out the other docs too.

Our Z pros will have some input for you. Meanwhile, sign in, go to User CP menu (upper left), click Edit Signature and add your Z model, year, shifter, turbo or NA, mileage, etc. Saves you having to add it every post. (Guys go crazy here if you don't lock your Q to your specific Z every time you post...) Then click Edit Avatar and add a little Z pic under your nick. Cool? You are solid here.

So, Mr. Rocha, just clarify which model you have first - and the pros here will help you.

Thanks and welcome! :icon_super:

Someone may correct me, but your oil pressure issues shouldn't have anything to do with vacuum.

Your cruise control may or may not have anything to do with vacuum. But it is likely given your other issues.

The vacuum system looks scary but it isn't really all that bad.

In principle, all of your vacuum starts at the INTAKE manifold and is just a series of branch circuits from there. I assume that is what you meant when you said you tried at the two ports on the exhaust manifold.

First things first. Do you still have all of those vacuum lines unattached? Since you have already pulled everything apart, you need to cap off any open lines, as they are giving you a big honkin vacuum leak. (Good luck getting everything back together right. You will definitely need an FSM for that) Once you do that, take your time and work backwards to find the first/primary leak.

It works like this, your engine is basically a big air pump that is driven by lots of little explosions. Air comes in through the intake (vacuum pressure) and goes out through the exhaust. If the engine is running you have to have vacuum at the intake.

The more leaks you have, the lower your overall vacuum system pressure will be at any one point. Thought experiment: If your are sucking 100 psi through one hole, how much pressure do you have at that hole? What about sucking 100 psi through 10 holes?

Lots of things can affect the amount of vacuum you are getting at the end of the line, in this case your HVAC controls. The most likely scenario is a disconnected or rotten line at a point in the system closer to the source (your intake manifold) than where you are trying to "measure" it.

It is a little backward but this may help. You have a water hose with a big hole halfway down it. All of the water is going to go out of that hole intead of the nozzle at the end.

Good luck and welcome to the forum.

This may help as well to clear your thinking on it. Plug one of the two holes you are using on your intake. With the engine running, spray a SMALL amount of starting fluid into the air around the other manifold port. You should hear the engine rev up as this is the same thing as giving it some gas.

If it doesn't work, then you may actually have the inside of your manifold all agummed up and the port really isn't a vacuum source any more. I doubt that the ports actually are blocked, but you never know...

Sorry intake manifold, I am still learning. I have replaced all of the vacuum lines leading to the vacuum tank to the manifold and the selector, but nothing has helped much. Is there another way to test it.

Check out this web page on testing vacuums, etc. Maybe something there to help you.

http://www.atlanticz.ca/zclub/techtips/vacuum/

Assuming when you took everything apart and put new lines under the dash, and hooked them up correctly. Take the vacuum line from the vacuum tank and put it directly to the manifold. Start it up and you should hear the an actuator shut. Try using the vent selector and see if everything works. My assumption is you don't have the vacuum lines right, or a line came off when you put it all back together.

This may help if you don't have it already.
http://www.xenons130.com/images/Auto...nversion10.png

Great link! I bookmarked this one for myself :icon_super:

It is pretty cool, but obvious when you think about it, that vacuum testing can give you many of the same results as compression testing, sometimes more accurately, and even give you other indications, like exhaust restriction.