Hard to tell from that pic... Start simple. Take a pic of your HVAC controls. Does it have a setting for A/C or not? 

Here's a pic of a non-AC control head:

 

And here's an example what it looks like if you have factory air:

A picture of the AC compressor would probably tell something.  And the throttle linkage.  The factory setup has a vacuum controlled idle speed enhancer for when the compressor is loading the engine.  The AC condenser in front of the radiator would also be a clue.

The panel @Captain Obviousposted is dead on identifying exactly what is installed. Also the vacuum bottle and solenoids on the passenger side strut tower

The 1976 FSM has a complete and separate chapter dedicated to the AC system.  The 1975 FSM does not appear to have it.  Probably worthwhile to download the 1976 manual and take a look.

 

Thanks for the indicators - mine is definitely not factory, the control panel does not say AC, and the AC binary switch is mounted below between the CA warnings for Floor Temp & Cat.

I took a pic, but it's out of focus.

All the lines on mine have the hose clamps, definitely generic, not factory fitted lines.

I'll download the 76 AC section & review it. What I'm inclined to do- since the major comments need replacing - is what I did with my X1/9, convert it to Orifice tube/Accumulator, and ditch the expansion valve & receiver drier. Just have to figure out what to use as a controller.

Pics in the future would help us out tremendously. Could have answered your question in a couple of posts. Keep pushing on friend.

On 7/5/2018 at 11:04 AM, siteunseen said:

Thank You!

I will most likely put it off the head hose as that is what feeds the core according to this flow diagram.

Can't seem to find any concise pics of the overall layout on the 280Z - mine has a loop hose that connects the t/stat housing to the water inlet housing. No pic of it in the 75 FSM.

Unclear as to the point of that, unless it serves as the bypass to circulate the head & block when T/stat is closed. Seems like an unwieldy design though.

Any ideas?

 

19 minutes ago, HusseinHolland said:

Can't seem to find any concise pics of the overall layout on the 280Z - mine has a loop hose that connects the t/stat housing to the water inlet housing. No pic of it in the 75 FSM.

Unclear as to the point of that, unless it serves as the bypass to circulate the head & block when T/stat is closed. Seems like an unwieldy design though.

Any ideas?

 

There is no coolant bypass. When the watercock valve is closed, it is deadheaded.

5 minutes ago, SteveJ said:

There is no coolant bypass. When the watercock valve is closed, it is deadheaded.

So, what is the point of the loop? You are familiar with what I'm talking about? I assume all 280Z have it. Not talking about the heater circuit.

Edited March 31, 20231 yr by HusseinHolland

The thermostat has a weep hole for some coolant to pass before the t-stat opens.

Here's the 280Z t-stat housing. This drawing shows the EFI sensors and switch.

I think I found what you are referring to.

Here are most of the part numbers in that drawing:

No, I didn't see any mention of this in the 75, 76, or 78 FSM.

40 minutes ago, HusseinHolland said:

Unclear as to the point of that, unless it serves as the bypass to circulate the head & block when T/stat is closed. Seems like an unwieldy design though.

Any ideas?

I think that might be the purpose.  Not clear how many 280Z's or 260Z's or 240Z's had it or why nissan stopped using it.  I've seen it discussed before thoguh.

ZCD sells them and some people put a T in the return hose from the heater core.  https://zcardepot.com/products/coolant-hose-engine-bay-t-fitting-280z-280zx

Here's a good place to browse if you want to see what things are supposed to look like.  Sounds like you have an aftermarket AC system.

https://bringatrailer.com/listing/1975-datsun-280z-22-13/

Looks like they were only used for a short time period.

https://jdm-car-parts.com/products/water-inlet-lower-radiator-hose-rh-front-of-engine-datsun-280z-1975-5-1976?variant=27526042633