1986 300zx with digital dash and air climate controls. A/C does not work and it constantly blows out heat whether air is turned on or not. Nissan mechanics can't figure it out? Any suggestions?

Asked by Feb 13, 2012 at 12:31 PM about the 1986 Nissan 300ZX

Question type: Maintenance & Repair

I bought a 1986 Nissan 300zx about 4 or 5 years ago. Dash and controls are
completely digital.  Air conditioning never worked right from the start. In addition, it
constantly blows out heat whether the air is on or not. It has been to two Nissan
dealerships for repairs and neither dealer could figure out what is causing the issue.
Any suggestions would be greatly appreciated

12 Answers

445

More than likely the reason that Nissan can't figure it out is because most of their techs today have never worked on a vacuum based system. I would recommend a specialty shop like Specialty Z or other Z specific shop. I googled 86 300zx ac repair and came up with a lot of insights. Here are just 2 that I found: http://wiki.answers.com/Q/How_do_you_repair_a_1986_Nissan_300ZX_that_ blows_hot_air_even_on_the_AC_setting http://townhall-talk.edmunds.com/direct/view/.f0de3e1 I hope those are helpful... other helpful sites are Zcar.com and 300zxclub.com. Always use the "search" function at those sites first to see what you can find...if no luck ask this same question in the appropriate forum. If this has been helpful, please click the "helpful" button below. :)

17 out of 17 people think this is helpful.

The heater/climate control in that car has its own computer for one thing. The temperature sensor is in the roof by the windshield, between the t-tops. There is a plastic cover and under that is a small fan with a couple of wire sensors coming off of it. I would check that. Be careful to not remove it if you don't have to because they are kind of a pain to put back in correctly. Other than that, are you familiar with how to adjust it?

6 out of 6 people think this is helpful.
190

jdawg... I've had two 86 300ZXs since 2000 and I've had to overhaul the climate controls on both of them because of the exact same problem you have. The climate control uses three vacuum servos to change the position of the air doors in the climate control box, controlling both air temp and air flow. Since these cars are now 20-25yrs old, the rubber in the servos has dried out, cracked and no longer work. They have to be replaced, and its a good idea to replace all the vacuum hose around the climate control box too. If you KNOW you have good vacuum at the vacuum solenoids just above the accelerator pedal, then this is the problem. This is a major interior teardown. Both seats, the steering wheel and the entire dashboard have to be removed to gain access to the climate control box. Luckily, with the steering wheel and seats removed, all you have to do is unbolt the dashboard (2 on each side, two under the console, and eight along the defroster vents), unplug 3 harness plugs at both ends, then pick up the dash and walk out with it completely intact. At this point the climate control box can be unbolted from the firewall and transmission hump, unplugged and pulled from the car. There's one servo on the left side and one servo on the back (which is why it has to be removed to be worked on... sigh) The third servo is intake air recirc and is on the blower air box next to the passenger door. I figured this all out using the factory service manual for the 86 300zx. This is an invaluable resource for doing your own troubleshooting and repairs. And it can be downloaded for free off the internet.

12 out of 12 people think this is helpful.
65

Can you tell me where to get the servos, does Nissan still sell them or an aftermarket part. I have an 85 2+2 and parts are getting hard to come by. I am the original owner by the way. - Thanks George

2 out of 2 people think this is helpful.
190

George... I go to two places for my parts. First is www.300zxpartsforyou.com This is a site run by a great guy named Steve Berman in San Bernadino, CA. He parts out 300ZXs and has piles of hard to find parts, including these servos. The second place is www.courtesyparts.com, the parts site for Courtesy Nissan just outside of Dallas, Texas. If one doesn't have the parts I need, the other usually does. Another great resource is www.z31.com. In addition to a forum and lot of maint and repair info, they also have a complete copy of the z31 300zx parts microfiche on line. Its hard to get around in, but usually you can find the part number of what you're looking for so you can search the internet for it.

7 out of 7 people think this is helpful.

dash pots on heater box have holes,or a broken vacuum hose

1 out of 1 people think this is helpful.

the heater control valve is shut of by direct vacuum

1 out of 1 people think this is helpful.
25

The hose on this heater control valve gets brittle and breaks. Probably the first place to look - in the engine compartment - if your blower just puts out hot air all the time. This is an easy check.

2 out of 2 people think this is helpful.
1,185

Ok fixing hvac 101. I have one of these and just fixed mine. On the back of the plenum run a main vac line to the round canister you'll see a nipple w a half moon stamped m under it the other line opposite on canister goes to heater dash pots (the line through fire wall) the switch on the canister (bottom) goes to heater control valve.

4 out of 4 people think this is helpful.
1,185

Canister is located behind passenger headlight

2 out of 2 people think this is helpful.
20

my mechanic installed a dedicated vacuum pump to the ac and it quit blowing hot defrost and is like new. May have to adjust to allow for heat in winter.......

2 out of 2 people think this is helpful.

I can't post pictures on the vac hose connections. 84-89 Nissan tech help and fix it on fb I have tech tips daily.

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