The DREADED Auto Air - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 4 (permalink) Old 09-04-2019, 08:56 PM Thread Starter
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The DREADED Auto Air

Hello all! I have been reading in the shadows for some months now and have finally hit a wall that has caused me to sign up for this forum. I have a 1980 280zx that I am try to restore. It is a solid car and runs well however, I live in Alabama so a good climate control system is a must. My system seems to have a set of symptoms that are different than all the posts I could find on the topic so here goes...

My AC can blow quite cold and my heat quite hot. It seems that I can only get the AC to blow out of my vents when in the full cold position and it will sometimes close. But then if I switch it out of max cold and back in, it will blow cold out of the vents again. I have replaced over 20 feet of vacuum line in the car and am starting to get frustrated as I am 6’3” and working on this car is not a tall man’s game. All input appreciated. I would love to keep the original system in the vehicle but know some of you may recomend I switch to manual air. If you think this could you tell me why?
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post #2 of 4 (permalink) Old 09-05-2019, 02:46 AM
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no reason for you to "have to" sign up for this forum. its free. you own a Z and you owe it to yourself and your car to spend some time on here. its a great reference for everyone and there's still some decent folks on here who are willing to help others with issues. we are all willing to help. having said that, the next thing i will say (and you already know what it is) is to yes, swap to the manual system. the auto systems work a bit differently and unfortunately you are at the mercy of the auto system to set the temperature where it thinks it should be. i have had some of the same issues on my Z31.

exactly which vacuum lines have you replaced? there are a lot more little solenoids and other junk behind the dash that operate the complex auto-climate system in these cars, and usually if one or more stops working, the AC starts functioning wierd. this is why it is just easier to do the swap. have you looked into diagnosing the system via the 1980 FSM? if not, head over to, S130 section and download it for free. also readup on the troubleshooting section on the 280zx section on the website. there are some pretty good write ups there on how to fix climate issues and on the auto to manaul swap.

i understand the frustrations of being tall and working on a Z, especially under the dash. not fun. but it has to be done.
its already September, my recommendation is to go ahead and repair or swap the system when the cool season arrives. you can plan to have the car down for sometime and properly get in there and fix these issues before next summer. i mean, if you are in a position to do this. but first, try the basic troubleshooting via the book first and see what you can find out.


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post #3 of 4 (permalink) Old 09-06-2019, 10:26 AM Thread Starter
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Hey Bon! Thanks so much for the reply. I do have the FSM. I read through every post on this issue I could find in the forums and went through the diagnostics people and the FSM recommended first so as to not rehash a topic already covered. I’ve replaced every hose in the system. The system holds to a vacuum leak test. Then I started testing electrical issues and find that pretty much every component is out of tolerance based on the FSM. Looks like the swap is in my best bet as I will be driving this car a lot. Now to see who might have the parts!

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post #4 of 4 (permalink) Old 09-16-2019, 06:57 PM
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I had similar symptoms. In full cold position the air should blow out the front vents but at times you'll notice the air can cut out under load. There is a dashpot sometimes called the power servo that sits on top of the control unit and opens the air mix door when it receives vacuum, that is the door that also allows air to flow to the front vents. It needs to receive constant vacuum to hold that door open. In my case that pot went bad so it wasn't holding enough vacuum to keep the front vents open most of the time.
Even before checking that pot, one thing to check is that you have the lines to the right ports on the vacuum reserve canister. Finnicky front vent problems can also come about by having those lines reversed. One of them should go to your Fast Idle Control Device that sits on the intake manifold and is supposed to open an extra air bypass when the compressor is on to raise the idle. The other line through the firewall is what provides vacuum for the power servo. If you're getting air out the front vents when your A/C is on but not when you're in full cold Econ mode, those lines are probably mistakenly plugged into each other's ports on the canister. A quick way to check if you have it right is put the air in Econ mode and disconnect the vacuum line to the power servo at the vacuum canister, the front vents should immediately close. That line can also get easily cracked around the end where it meets the canister and even a tiny amount of loss on that line will cause the air mix door to close sometimes - same reason it'll cut out if you're going up a hill in 5th gear and there's not enough vacuum to hold it open.
Hope this helps, I had a ton of problems with mine but finally got it all sorted out...
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