Vacuum Pump

on a stock turbo car it gets bolted in the right front fender well, i believe the wires came from the right side horn harness. (non applicable to na cars, dont even try unless you want to replace and rewire a harness or two). when i did my na2t, i just mounted it in place of the vac canister, (removed the solenoid from the can and ran it up to the heater core valve) i had one hose coming off the pump, tee'd off by the watercock, one going to the solenoid for the watercock to the watercock, the other hose going in to the climate controls. i wired my pump to turn on in the "on/run" position..

since the na vac can does not have the pressure sensor, i deemed it worthless and got rid of it. to do the job properly you need to replace the body harnesses with that from a turbo car with a pump, install the pump, then the can with the pressure sensor. due to differences between years and na vs t cars, you will need to rewire the connectors connecting inner and outer chassis, and engine harness.

or, the best option: fix all leaks in the climate control vac system, replace any broken actuators, run new vac hoses, and run a new one way check valve before the vac can. this would eliminate the need for a vac pump until the lines/actuators wear out again. the check valve(s) prevent the boost from entering the system, keeping the vac pressurized. (the na can has a check valve in it, but it frequently fails, especially after 20+ years)

I've got a check valve and it still kicks the AC to defrost and heat on boost. Does the pressure switch you are talking about run into the ECU or other controls at all (hence the need for the wiring harness) or is it pretty much stand alone and just needs ACC power? If it's just ACC power I can tap into the ACC power where I tapped for the elec fan since it is right there. I may have a vacuum leak but all the hoses from the plenum to the canister to the ac lines are all brand new and I am fairly certain that I don't have a leak there. I believe what is happening is that the canister is loosing it's vacuum and equalizing with atmosphere when the check valve is forced shut by the boost. Then again, the check valve may be shitty, too. I'll give everything a once over. Now that I'm back in the US, I can find things like ether to check for vacuum leaks. As soon as my air compressor gets through customs, I'll do a positive air pressure test to make track down any leaks, too. I am fairly certain that the ASCO plenum spacer is leaking also, I'm having issues with my CAS and everytime it backfires I see smoke from under the intake manifold. I'm going to reseal everything when I get my new injectors in. In my rush to get the car running so I could ship it, I installed 85 injectors with resistors and ever since I've had horrible failures one after another. First the MAF blew, then the ECU, and now the CAS looks to be bad.

If the ac goes hot you either have a leak somewhere or a faulty check valve. it should not do that, a properly functioning system will hold vacuum until ignition is turned off, then the solenoids under dash release pressure.
The pressure switch and vac pump wires are in the exterior body harness on turbo models, but were not in the non turbo models. (saves nissan money on wires) the wires all lead to ignition and to the relay box underhood (hence a vac pump relay).
like i said, i wired my pump to the on switch so it came on when engine is on, i didnt need the pressure switch or anything, just the pump.

there are about 12 lines under the dash, and several actuators (all of which can leak) the most prone one to leaking is the recirculation actuator.

you need to be extra careful and take your time. none of this is a one day thing. it took me two days to remove and replace everything (being extra careful, checking all wires and hoses, replacing everything possibly broken)

now theoretically, you could manually wire in the pump and pressure switch. i think its something like b+ to ignition, ignition to pressure switch, pressure switch to relay trigger, trigger to ground. then b+ to relay switched, switched to pump, pump to ground. (dont take this to heart, i havent looked at the wiring diagrams in almost a year as i deemed the switch unneccesary. running the pump all the time never really hurt the pump nor yeilded any slowed performance of the system. i just dissasemble and oil the pump every 6 months to a year. [about 80k miles running that way])

i plan on running it the same way again when i get my restoration complete.