lazarus2297

Honestly I hesitate to ask this here, because I feel the only answer I will get is "read the FSM". That being said... I have a question to help my troubleshooting.. PO of my car deleted the entire AC system and cruise control. I am not looking to get the AC working at this point, but I would like the system to at least circulate air.. At the moment the fan works (albeit oddly loud) but I can only get air to come out of the defrost vents.. I had the dash out and manually opened the diverter and it is physically able to move.. I traced the vacuum line and there were no breaks or anything.. I am not 100% sure how all of it is supposed to work, but I assume its ultimately powered by the vacuum pump in the engine bay.. Anyway I thought I would ask here if there was a known "problem" part I should start with first. By they way I have an 86 turbo with digital climate controls.
Thanks for any advice!

rogerz

vacuum pump only operates when under boost. the normal mode is the vacuum comes from the plenum. the vac pump is under the right headlight but that is not your problem. There is a vacuum tank on the right side forward up high if you lean on the car with your hands on it your left hand will be close to it. There is a hose (original white) from the plenum to the vac tank port marked M. there was a blue marked line from the vac tank to the coolant control valve. should be some electrical looking thing on that port. the big port is for the cruise control and the one that is left used to be a red hose going thru the firewall to the controls in the car. the fsm has this info in it. once you get into the cabin thru the firewall the hoses are usually good only the engine room ones go out from heat etc. if you look forward from about seat height you should see a hose tee that goes right left. that is where you hook up from the vac tank. May have to remove a couple of plastic trim pieces to see it. more info in the fsm have fun. if yours is light blu gray you have the twin to mine.

Take the schematic from the FSM down to kinkos and have them blow it up to 11x17. Much easier to read unless you are a keen eyed twenty something. get fsm at xenonzcar.com

lazarus2297

thanks for the helpful reply, I notice the vac pump makes a constant noise when the car is in the ACC position and when runnning..

I will take the info you gave me on the color lines and the vacuum coming from the plenum and do some more research/checking tomorrow.

I did notice that all the color marked lines are very rigid, is that relatively normal?

rogerz

means they are shot probably. just run new ones after 30 years they aren't in good shape. if the vacuum pump runs all the time you are not getting vacuum to the vac tank or the switch that turns on the vac pump is bad. located in the vac tank. chances are you aren't getting vac to the tank. should be a line from M to a port on the rear (usually) of the plenum get a vacuum gage and hook it into the system to see what is happening. Maybe you got some massive vac leak. unlikely as the engine would run terribly. probably the moron PO left something open so the vac tank is likely at zero psi gage (atmospheric pressure) if you don't understand that try googling Psia and Psig.

Psi gage (what we usually refer to) Psi absolute (what we refer to often as vacuum)

Since the car has been totally fubarred by a moron you might want to just run a vacuum line direct into the cabin. disconnect the wires coming off the bottom of the vac tank and then the vac pump will not run.

lazarus2297

I will once again say thank you for being helpful!!

So if I run a line to the cabin, what would I hook the other end into in the engine bay? Would I just hook it to the plenum where the white striped line is currently hooked, since by unplugging the vac tank that line is useless anyway, correct? I mean my understanding is that, that vac tank controls cabin AC controls, Watercock Heater Valve, and cruise. So "deleting" it at this point isn't going to cause any performance issues.

lazarus2297

So I took did a couple pics and edited them to ask questions..

lazarus2297

so i found something I think to be semi useful.. when I take the vac line off the port on the plenum and put my finger over it the vac pump will shut off.. that leads me to think there is some leak on the plenum side but I don't hear anything (although to be honest it's kinda hard to hear anything over the vac pump.. ) and I don't see anything obviously missing.. Where would be a good place to start looking for the vacuum leak on the plenum side?

Thanks again in advance!

rogerz

the vac pump is only operated by the switch on the vac tank unless previous moron did something even more incredibly stupid. Plugging the port on the plenum is probably where you should run a vacuum line into the cabin from. why it would start the vac pump is a mystery only the PO can answer. Probably the hose is so bad that plugging it off causes the vac pump to make enough vacuum to switch it off normally. you are confusing cause and effect. the hole is normal on the bottom. the blue hose goes to the electrical thingy with two wires coming off it. often the port nipple gets broken off by some moron so if there is a hole there then the nipple is broken off. the electrical thingy is a solenoid valve that feeds vacuum to the coolant valve. vacuum keeps it closed no vac wide open. you said cruise and other stuff already gone due to PO so what is the issue. you said you want the fan to work and the only thing that moves the vent doors is vacuum., set of like 5 black cylinders under the steering column if you look up into the dash. Between me and the fsm you should have your answers. other possibility is that the control unit above the radio is shot.

those striped hoses are shot most likely. 30 years old replace everything. maybe it works but all the hoses are shot.

lazarus2297

Well you are correct in that honestly my main concern is getting the cabin controls to work, and since the cruise is physically gone I am not terribly concerned with that aspect of it working. I guess the reason I ask about the leak is that when all the other lines are plugged or capped, and the line going to the plenum is attached like normal the vac pump runs endlessly, when I remove the line from the plenum and cover the vac line with my finger the pump gets enough vacuum to stop running.. So I was concerned that would indicate a vacuum leak "up stream" from the port on the plenum. I should be able to at least test the line into the cabin tonight, to see if that makes the cabin AC controls work properly (minus AC).

lazarus2297

ugh..... so no all of a sudden my mph and rpm display on my dash are black.. Nothing I messed with should have affected my dash and I have had no signs of power supply going out.. I did run a very rudimentary attempt at a test vac line to the cabin with no success.. I tried manually moving the billows under the steering wheel and that is near the dash, but was like crazy rough.. So other than power supply or actual dash failing.. is there something I could have unplugged, or bumped that would have caused those to displays to go blank? Or did I just have one of the worst coincidences ever..

rogerz

the dash power supply is right in there where those vacuum motors are so possibly you knocked a connector loose. if you got a significant vac leak then your idle should be funny. one way to look is use an unlit propane torch with the valve open and wave it around places where you might get a vac leak. idle increase means you are sucking in propane thru the leak. remember under normal operation the vacuum operator stuff is only affected under boost. At 60 cruising down the hiway my engine is pulling like 16 inches of mercury.

zxguy1986

Laz: I had the same problem with my air distribution on the interior in my '86na: air came only from the defroster. I figured that was the default position of the dampers, vacuum operation, etc. If not working right, air distrib comes from the defroster, no matter where the slide selector is set. So it's a common problem, I see.

So I replaced all the vacuum hoses per the FSM (diameter is important) and eventually found a used vacuum pump, too, at a recycler's yard. (Check out car-part.com, sort search results by zip code) Plus, check and clean every connection from the main harness to the pump and dash. I solved the problem perfectly. Air distrib now from all dash and side vents, floor, and the defroster only when selected, just like new! The '86na is a masterpiece of design and assembly. Almost the perfect car, if you ask me. I would marry it but not allowed in my state. Will have to move South to do that. Plus, my bed isn't really big enough.

lazarus2297

So I have replaced all vacuum lines. I now can verify that I have vacuum in the cabin, but i have still no real success so I think it might be the actual hardware in the cabin. Here is how I think the vac systems works in regards to the vac tank and ac controls can anyone confirm?

Vac tank has 2 sides, one with a hose that goes to the vac pump, the other side has 4 "ports".

vacuum to the cruise, cabin controls, heatercock valve.

vacuum from the plenum labeled "m".

I assume the vacuum to the cabin controls and cruise is "always on" and the device/s on the other end work off that, and the vacuum to the heatercock valve is "switched".

The vac pump is responsible for the vacuum when the car is off and then it turns that duty over to the line coming from the plenum, when the car is running. Therefore the vac pump should not be running when the car is running..

If all this is correct I will work off that for further diagnosis of the cabin controls. When I have the dash shell out again.

Robin Hood

I am having the same problem with my Nissan 1987 300ZX Turbo. Only hot air blowing out of the defrost vents... Did you solve you problem?