Mikey8907

I'm a new Z owner, i bought an 86 2+2 non turbo January 1 as my first ever project car. And among a list of things i want to fix the one that is keeping me from driving the car comfortably is the defroster is stuck on. I have seen a lot of posts on this and everyone says its the vacuum hoses and while i did find a few holes i have since replaced all the hoses in the engine compartment. The water **** valve is not getting any suction so it is either the solenoid valve on the vacuum tank or the control unit itself not sending the signal. I found a another vacuum tank in a junk yard but either I'm unlucky and that solenoid valve is also broken or its the unit. On the control unit no matter what buttons i push it will not change off of defrost i can turn the fan on and off but that's it. Is there away to test either the valve or the unit with out just buying a new one and hoping for the best?

Thanks
Michael

SwarthyOne

did you check the hoses under the dash as well? you should have one that goes from the tank by the passenger headlight through the firewall and connects behind and above the glove box.

zxguy1986

Just for the hell of it, there is a slider switch at your knee on the face of the under-dash closure panel. See it? It's supposed to open/close the air feed to your feet - if your vacuum dampers are all working right, etc.

First, make a note of what position that switch is in (up or down) now. Turn the motor on, idle the car, run the heater and blower so your air is coming out of the defroster full blast. Then slide that switch by your knee up and down a couple of times - and then leave it in the OTHER position from where it was before you started the car. Push the various air-distrib buttons on the AC/heater panel.

Let me know if this makes any change to your air outputs at the dash vents and defroster. If so, you solved the problem for the moment. All your air-distrib buttons on the heater panel will work now. If not, there are a couple of other tricks to try. Report back, please. Maybe we can figure this out. (I have an 86NA)

Mikey8907

Sorry for the long delay in replying was out of town and then got sick, But to answer both of the above questions. I could not find the switch you’re talking about but while I had my head under the dash I found one or two vacuum tubes that where not connected to anything so I took the dash off and most of the air passages now I am left with what I think is the heater core that is in the center of the dash (behind where the radio and climate control unit was), what I think is the AC Condenser box to the right of that, and the blower unit to the right of that. I have the diagram for where the vacuum tubes are supposed to go but I don’t know if the solenoid valves are labeled. I plan to work on it this weekend if anyone has pictures of what I need to do to replace all the tubes and maybe clean the heater core and condenser while I have everything tore apart so I don't have to do this again.

Thank you
Michael

zxguy1986

OK, hard to miss that slide switch. I think it's the only thing on the surface of the panel between your knee and the steering column. It's on page HA-5 of your service manual. You DLd it at http://www.xenonzcar.com/z31/reference.html

Anyway, may as well replace all your vacuum lines now that you prepped for it. They are full of holes and splits if original. Check out thumper's page:

Vacuum Lines

Get the materials you need (try to get the right diameters as shown on the list - it makes a difference in the vacuum pressure/response time) and replace them one hose at a time, removing one end, putting the new one on and tracing the old one to the other end. Otherwise you will get lost.

While you are inside the dash, make sure the drain for the condenser is clear of dirt and crap, clean the dust clumps off the condenser face, test the drain there with a little water. It should drip out onto the ground behind the front left wheel. Check any damper doors you can access to make sure they are clear for movement. That was a lot of work to get the dash up and off. Good time to replace any dead bulbs in your gauge cluster.

Let us know how it goes. Once all your vacuum lines are new and connected, the air distrib should work right.

Mikey8907

Ok so good news and bad news, I got everything out checked all of the vacuum tubes and they are good. I did however find a couple ones that were not connected and reconnected those. So the good news is the Recirculate works now so maybe I can turn it on and stop it from blowing hot air in while the car is moving. Also the floor vent actuates correctly now. But I still have the original problem of only getting hot air out of the defroster. I think it is control unit that is the problem. I will take it to the Nissan dealer once I get some money to throw at it, unless y'all have another way to test it.

Thanks
Michael

zxguy1986

Welcome back. Not sure what 'control unit' you mean. The dampers and gates respond to the changes in pressure in your vacuum lines. If your lines are all good and connected right and your vacuum pump(s) are working, air should go where you direct it by your on-dash switches and buttons.

When you say you might take it to a Nissan dealer, I wonder if they would handle it for you. Around here, it has been at least 10 years since any dealership had even one guy who knew anything at all about the Z31. So they would charge you by the hour whether or not they even diagnose the problem or fix it for you. I bet you can solve it yourself and save a pile of $$$.

Mikey8907

Well I have tested all the vacuum tubes with a hand pump and all acuate like they should, i have also tested the Solinoid that controlls the water **** valve and it works as well but when i plug the control unit (the computer that is in the dash above the radio) in i still have the same problem. The defrost indicator light on the control unit stays on no matter what button you push. I went ahead and ordered a replacement from 300zxpartsforyou.com so hopfully that will work ill post again when it comes in.

zxguy1986

OK, I'm guessing that you DLd your factory service manual (FSM) at
XenonZ31 Reference
and you went through Section HA to locate the AC/Heater troubleshooting sections for your Z31 model (HA-44 to 48?).

If you go through those steps one at a time you will know that system well. If you haven't done that, do it before you take your next step. You're getting closer but it's hard to help from here. You can just decide to fix it before you close it up again and not give up. I guess when all else fails, we have to read the instructions - if you haven't already read them. Definitely report back when you solve it. Thks.

BTW, does your AC work now, pushing cooled air up through your defrost? And your air temp slider switch? All are working? The air speed slider switch works? Your problem is only that you are stuck in defrost mode, you cannot send air through your dash and floor vents, right?

Oh yeah, what is your Z's original mileage? Thks.