No heat

[arcdef]

Hey,

I am trying to establish why my 260z's heater does not work. The cables seem to be functioning correctly and moving in a full range but heat never arrives even when engine is up to temperature. I have taken a few photos, can you see if everything looks right or point me in the direction of what to do/check. 

 

Only thing I noticed that could be wrong is that nothing is connected to this?

Other than brackets being corroded does the rest look correct?

this is when set to heat

this is when set to cold

 

Thanks,

 

Ash

[Captain Obvious]

Looking at the pics, it appears that your 260 came with A/C. If that is correct, there's vacuum involved.

34 minutes ago, arcdef said:

Only thing I noticed that could be wrong is that nothing is connected to this?

That unconnected device is what Datsun called a "vacuum cokk", and it's purpose was to block all the water flowing through the heater core under some circumstances (like you had the A/C on). It's set-up dead-man switch style and is closed if there is no vacuum present. So yes... That could a reason you aren't getting any heat. There could be lots of other reasons as well, but I'd start with that one.

Take a look at the 74 FSM (Factory Service Manual) in the Air-Conditioning section. It explains the function of that vacuum cokk.

What is the current state of the system? Vacuum lines present and recently replaced? Vacuum lines present but old and leaky? Vacuum lines non-existent? No idea what I'm talking about at all?

[arcdef]

Interesting. So I assume these are the start of the vacuum lines?

 

And this is where they end right now ?‍♂️

Not traced the passenger side but my guess is they go nowhere. Is there a way to bypass this system.of is it just a case of plugging them back in and the system will work again? Where does the system get its feed from?

 

Thanks!

[Captain Obvious]

Yup. Those are the vacuum lines that are supposed to control the system. Although I'm not sure about the use of the word "start". Semantics, but for me, the "start" of the vacuum lines system is up in the engine compartment. My guess is that the ones that are there are dried out, brittle, and have lots of leaks. And what isn't leaking right now, will be as soon as you bump it.

12 minutes ago, arcdef said:

That thing in the pic above is a vacuum switch. It's a little valve that directs vacuum line to the appropriate destinations based on the position of the heater control lever.

The vacuum line marked "S" is "SOURCE" and it's supposed to be the vacuum source coming from the engine. Up in the engine compartment is supposed to be a vacuum reservoir and a couple little "magnet valves" (solenoid valves) to control the routing of the vacuum. Is any of that stuff present up in the engine bay?

The vacuum line marked "D1" is supposed to go to that vacuum cokk on the heater core water line.

You really need a copy of the FSM. Download one and read through the A/C section.

Out of curiosity, what year is your 260? In the US, the only answer would be "1974", but I think in other parts of the world, the answer could be anything from 74 to 78. I don't know what the UK got.

You could probably "bypass" most of the system by running one dedicated vacuum line, but might depend on the year.

 

[arcdef]

Yeah this a '76, was originally LHD but converted to RHD. It has also had an engine change and the vacuum reservoir is no longer there. Sorry to be a pain but what steps could I take to bypass/eliminate this so the heater can work again? Can I force the vacuum cokk to stay open?

Thanks

[Captain Obvious]

OK. So no vacuum reservoir, no magnet valves, no nuthin'.

You should be able to connect a vacuum line from the intake manifold directly to that vacuum cokk. In theory, any time the engine is running and there's manifold vacuum, that vacuum cokk should be open.

If you floor it, you're likely to lose vacuum and the cokk could close, but I suspect that's the least of your worries.

So before you go through the effort to run a new piece of tube through the firewall, you could test the theory with just a small piece of tubing and mouth vacuum. I don't know how much vacuum it takes to open that valve (especially one that's been shut for years and may be stuck), but if it's not a lot of vacuum required, you might be able to open it manually.

[arcdef]

Yeah literally only the master cylinder left. 

I will give that ago using my mouth over the weekend and see if it works!

Thanks for your help!

Ash

[AK260]

Yeah literally only the master cylinder left. 

Wow! That V8 sits squarely behind the front axle!! Very nicely done sir [emoji106][emoji106]

[arcdef]

I can't take credit for that I'm afraid. The previous owner done a very nice job of it though!

[wal280z]

7 hours ago, arcdef said:

I am trying to establish why my 260z's heater does not work. The cables seem to be functioning correctly and moving in a full range but heat never arrives even when engine is up to temperature. I have taken a few photos, can you see if everything looks right or point me in the direction of what to do/check. 

 

Only thing I noticed that could be wrong is that nothing is connected to this?

Other than brackets being corroded does the rest look correct?

this is when set to heat

this is when set to cold

The heat selector appears to be functioning correctly. It appears as though the missing vacuum line is for the recirc / fresh air intake.

The vacuum controlled water cokk would be in the closed position, as mentioned previously.

7 hours ago, arcdef said:

And this is where they end right now ?‍♂️

 

Do you have a MIGHTY VAC or similar? Hook up the non-connected vacuum line WITH THE ROUND GROMMET lying on the floorboard to engine vacuum. That should be the source line that would normally be connected to the magnet valves @Captain Obvious has mentioned.

Move the mode selector to HEAT or DEFROST.  Move the temperature to HOT

When vacuum is applied, the small flaps should open (as well as moving the internal flap which directs the airflow over the heater core). Note, the defroster tubes *SHOULD* be connected to the heater box cabin side of those small flaps.

Do you feel heat?

Download the FSM as suggested, it has a wealth of diagrams to show what flaps are in what position for normal operation.

 

Might need to take another picture on the OTHER side of the heater box.

 

Edited March 19, 2020 by wal280z
edit in bold

[Patcon]

I was thinking MityVac too. Brake bleeding vacuum tool...

[Zed Head]

8 hours ago, arcdef said:

Yeah literally only the master cylinder left. 

 

I will give that ago using my mouth over the weekend and see if it works!

Thanks for your help!

Ash

If you're not planning to reinstall a vacuum bottle it's kind of moot.  Pointless.  Can't really drive around sucking on a tube to get heat.