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JTCN

1975 280z Heater Not Working

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It snowed today in Louisiana and it reminded me that my heat hasn't been working, currently typing with numb fingers.

Here's what I know: No heat comes out of any vents no matter what setting. Outside temp air is blowing through the center vents and the side vents no matter the setting.

I got the car to operating temp and felt the heater hoses to the firewall, both were hot to the touch.

I checked the vacuum lines from the manifold to the heater solenoids and they were connected fine. The line from the solenoids to the firewall is fine too. (Haven't checked inside dash yet.)

It's possible that I might've unplugged a vacuum line that runs under the dash to the AC/Heater unit. I've pulled my radio and my center console out plenty of times. Might've snagged something.

 

Since I have hot coolant flowing through the heater core and the hoses I don't think it's a heater core issue. I'm suspecting the climate control panel or something connected to it.

It's my understanding that when you switch your climate control to heat/defroster it should immediately pump air through the defrost vents/floor vents. Mine always blows through the center and sides on any setting. Also, My lever that controls the "Hot/Cool" temp of the air coming through feels really bad and not properly set up. Hard to explain but it feels almost spongy and doesn't stay where I put it. I read that it's a cable that controls this and I might have to adjust it.

Also possible that the door that controls which air gets blown through the vents is stuck? Could the solenoids that control the heater be seized?

 

 

I haven't tried checking all of these yet because I'm really not looking forward to pull my dashboard out. I don't have a radio installed right now though so maybe I could access this through that hole?

I'm just looking for someone that maybe had issues similar to mine that could provide some insight. I HAVE got my heater to work ONCE before, and I don't know how I did it. It was last winter and it was a seriously cold night and it just worked. I had heat pumping through my defrost vents but nothing since then.

 

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Since you said that air is blowing through the center and side vents no matter what setting you have it on, then it is clear that your vent controls are not operating properly.  The vent controls are operated using engine vacuum, so if you have a leak somewhere in the system then your vents will not open/close properly.  This is a common issue.  Run through the HVAC vacuum diagram in the FSM and see if you can find the leak.  The system has a lot of vacuum lines that can become brittle with age and crack.  If you check all your vacuum lines for the HVAC system and they all seem fine, then there could be something jamming the flaps that divert the air through the heater core.  Stick your head in there while you operate the levers and see if the flaps are moving. 

 

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This summer I had an antifreeze geyser in my passenger side footwell;

GF was NOT impressed      8)~~      I bypassed coolant lines to heater core in engine bay as a patch.

 

Looking in the Service and other Manuals, and various forums, I believe this (heater) system

 for these years,can be repaired,  without removing the dash. Although some say that it is quite a pain in the back - literally.

 

As with all things Z - there are quite a few "improvements" based on date code - I am 359550 Aug '76,

and my heater control valve/air control doors are control rod controlled only - Not vacuum.

 

It sounds like your issue may be seized, bent, broken or disconnected control cables, or a failed control valve,

or malfunctioning airflow transfer doors.

 

I'll be disassembling mine over the weekend, and may have some pictures, better info next week.

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Just got back from round 2. I can't stay out there for long because my fingers go numb and useless.

Anyway, I stuck my phone into the empty radio slot and recorded a video with my flash on. The cable to the temp lever is connected and works fine.

I could see the cable that's connected to the climate mode selector (REC, DEFROST, AC, etc.)

I could see pieces moving in there everytime I switched the mode. The cable was pulling them through the modes and they would click in place.

I was only able to see one vacuum line in there though and it was small and hooked up properly. I didn't feel or hear any vacuum leaks coming from there.

 

Is there any way for me to check the HVAC solenoids? Could they be seized? I followed all the vacuum lines going to them and they're all connected properly and not missing.

I found the lines from the manifold>vacuumtank>HVAC solenoids>line to the firewall. After that I can't tell.

I'll have to cut the tape around them to check if there's any tears/leaks along the lines but otherwise they're solid.

 

Edit: I cracked open my hayne's manual and it seems to me that some of the heater system is accessible through the glovebox? I'm going to try removing it and find out.

Edited by JTCN

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Alright I'm back from round 3 and we're finally getting somewhere.

I removed my glovebox and I can see clearly that when I move the mode select lever, the heater door opens. So no cable binding or broken cable issues there. 

So what is actually vacuum controlled? Are there seperate doors that use vacuum on 1975 cars?

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So I chased vacuum lines some more today and all the lines are fine.

I found all the lines from the manifold and dash pot to the solenoids, to the vacuum bottle, through the firewall, and under the heater controls.

Not a crack or split on any of them. All still soft and flexible.

 

I've done more research and it seems that on '75 cars the heater control valve is solely cable operated. No vacuum except for the flaps that control airflow.

Since the defroster/floor vents in my car never blow air on any setting, I'm guessing it's the vacuum controlled doors. But if all my vacuum lines are fine then what's the issue?

What do the HVAC solenoids actually do? How can I test them?

 

It's obviously a vacuum issue. The question is what's failing in the system to cause my problem.

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According to the image URL, this is a diagram of a 75

 

Image downloaded from http://www.atlanticz.ca/zclub/techtips/vacuumlines/ and rehosted here for longevity

75vacuum.gif

 

One solenoid controls AC fast idle (the plunger on your intake manifold, if you still have it), and the other seems to control on/off for the whole climate control system, I'm not sure what triggers that (maybe blower switch? I have to check a diagram)

 

The vacuum heater valve everyone is referencing is the "Vacuum cock" on this diagram, which is basically there to make sure you don't run the heater and AC at the same time.

Edited by ZHoob2004

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Well this is strange... lmao

I'm back outside after eating dinner and first thing I do is turn the key on. I heard the blower motor running and I was about to turn it off but decided to start the car anyway. For some reason I decided to feel over the defroster vent and oh my god theres warm air. I don't know how I fixed it but I guess I must've plugged in a vacuum line that I didn't notice was unplugged. I took them all off under the heater controls and plugged them into the right nipples on the hvac control unit.

 

I'm gonna shut the car off and come back later tonight to make sure it's still working LOL.

Maybe a datsun loving goblin came and fixed it while I was inside. Weird.

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16 hours ago, JTCN said:

So I chased vacuum lines some more today and all the lines are fine.

I found all the lines from the manifold and dash pot to the solenoids, to the vacuum bottle, through the firewall, and under the heater controls.

Not a crack or split on any of them. All still soft and flexible.

 

I've done more research and it seems that on '75 cars the heater control valve is solely cable operated. No vacuum except for the flaps that control airflow.

Since the defroster/floor vents in my car never blow air on any setting, I'm guessing it's the vacuum controlled doors. But if all my vacuum lines are fine then what's the issue?

What do the HVAC solenoids actually do? How can I test them?

 

It's obviously a vacuum issue. The question is what's failing in the system to cause my problem.

 

I rebuilt my hvac system and are in the process of putting it back together ... Make sure you are getting vaccum by pulling off the "S" hose off the selector and feel it with your finger... 

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