| Follow up from this: [ http://twinturbo.net/nissan/300zx/forums/general/view/2621241/Finally-installed-AC-lines.html ]
AC lines held vacuum up until a month ago when I charged the system. Unfortunately after charging and getting the low pressure side enough the compressor did not kick on. I bypassed the relay(jumpered) and the compressor kicked on and I started getting some cool.
So I had to break out the FSM for wiring and start figuring why the pressure switch wasn't causing the compressor to kick on. After digging around I found the pinouts needed and was able to verify I did not have wire continuity from the relay coil to the switch, but I did have continuity from the switch to the ECU sink/ground trigger. I ran a 12V jumper from the relay coil to the AC switch for testing, the AC system kicked on like it should so I verified a wire break between the relay and the switch. 
I also knew I had a wire break from the Intake Air Temperature(IAT) sensor which is behind the pass turn signal on the factory air inlet duct, both the supply and ground side wiring for this sensor had a break going up to the connectors by the fuse box, which is where the pressure switch wiring runs. (As a side note I installed a 2200 ohm resistor down at the ECU to trick it to read correct and turn off the CEL so I could pass an emissions test.
So with at least 3 broken wires I figured it was likely they were cut in the same place. I spent quite a bit of time with my fluke wire toner and pulling around on the main wire harness:
And got a rough idea where it might be, which was under the pass headlight. I started checking and pulling off tape and found this: 
Since under the pass headlight is a crappy place to work to solder I cut zip ties on the passenger harness and managed to get enough slack to pull it through into the engine bay: 
Then looking at it closer I found this:
 So I soldered them back together, and then heat shrunk over them, and double wrapped some with tape or a second later of heat shrink. 
With that done I put everything back together and test ran it, AC was making cold! Watching pressure at idle in driveway with redtek R12 replacement instead of R134a:
 Then I took it for a drive and noticed a repeating number on the odometer when I pulled back in the driveway.
One thing I noticed is that the cooling fan doesn't cycle for this setup, even when its really hot. The ECU will turn on one fan relay when the engine gets warm, but I'm not sure what turns on the other relay. Both windings work and the fan turns on, for high or low, but without the fan running and crawling in traffic or sitting at a light there is not enough airflow to get proper cooling on the condenser. Not sure if thats the way its supposed to work or what should kick the fan on for AC cooling purposes. I could run a jumper from the clutch relay to one of the fan relays so that anytime the AC clutch is on a fan relay is on, which would keep some airflow all the time, but that seems unnecessary.
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Finally got my AC going in my 96TT: - 
19:18:45 06/20/18
