R12 to R134a conversion, need a few tips

[hozzziii]

Alright I have to give you some backstory.
I have an '85 316. It has the 1.8L M10 engine. It did NOT come with AC from the factory.
The PO was my pops. And back in the day, he bought this AC kit from an Italian company named Diavia, specifically for this car.
I'm talking the whole ac system, with instructions and wiring diagrams and pictures, the whole thing. I can show you some pictures.

So, fast forward to today, I want good working AC, but this thing leaks, no surprise there.
So I have read the Detailed R134 Conversion thread and a few other sites and forums too, and I have started the conversion.

So far, I got a PF condenser, a fresh receiver drier, an R134a pressure switch with low and high pressure cut off, have not got the compressor out of the car and I still haven't got R134a hoses.
Ooh! I also bought a, I think Mercedes but looks really like E30s, expansion valve. But I'm on the fence about using the old R12 valve that came with the kit originally, but we'll get to that later.

So I have encountered 2 issues so far:

1) The old pressure switch has 4 wires going to it! and the new R134a switch I got has 2 connectors. This makes it tricky since even though I have the diagrams I'm not particularly sure I understand which circuit is doing what on this thing.
I wish it looked like a simple low pressure/high pressure side, but to me it looks like only one wire has positive current and the other 3 go to ground, eventually? If I sound confused, that's because I am.

So the Legend is the picture below, I recommend you take a good look at that too.
This is what I think I understand, so far:
From the AC Switch #16, power goes to the #25 Connector, to the #86 connector on the #6 Relay.
From that power goes to right side #27 connector behind the pressure switch #2. I assume if the condition on the pressure switch is met, then power is grounded.
As power is grounded, the other part of the #6 Relay closes, which means power goes from the Battery #5, through a Fuse #7, through the #6 Relay, to the Fan #1.

Alright this is where I get confused.
The left pair of wires on the #27 Connector, power goes through the bianco (white) wire through the magnetic clutch on the compressor, to ground.
This makes me think ok probably the other side of the left #27 with the Viola (violet) and Nero (black) wires has the positive current, right?
BUT THEN! That wire goes through the #25 connector to the Thermostat #13, and through the #14 Relay, and goes to ground on the other side?
Am I reading this right? Do I assume that opposite connections on a relay are the ends of the same circuit?

This is the part that doesn't make sense to me. There can't be two grounds on the same connector, you can't have current like that!
So that makes me think, Ok so maybe there is one positive current wire on the #2 Pressure Switch, and 3 grounds? Sounds very wrong, I am very very strongly suspecting I am wrong.

At the moment the drier and #2 switch are out of the car, along with the condenser and fan.
I think I can probably turn the car on, switch on the AC, and since the compressor is no longer getting power, I should be ok WHILE checking for voltages on the 4 ends on the #27 connector. see what I can understand.

And overall this brings me to the issue I am facing:
The new pressure switch has 2 terminals, I have 4 connections in the system, and looking at this map, I cannot safely say that its ok for my to just short two of the wires, and hook the other 2 up and call it a day.
Because each of these circuits does something different as far as I can tell, one controls that fan, the other seems to control the compressor, at least I think.
Part of me thinks "Ok how about I just connect two grounds to one end of the new switch, and one positive to the other end! That way I control both the fan AND the compressor with the same switch!"
BUT then I'm not sure which wire has positive current on the left #27 connector.

So yeah, any help would be appreciated.
If you need more information, I am more than happy to provide, pictures, anything.



2) The compressor is a Sanden 508. I mention this because funny enough I found a retrofit guide on their website while I was looking for information on the oil situation.
They provided some pretty useful steps on there, I'll attach the pdf if anyone is interested. The steps seem to be pretty generic to any conversion, not just specific Sanden compressors.
Disclaimer: I don't recommend you actually follow these steps if you don't have a Sanden compressor, but it gives a good general idea for you to know what is involved.
Anyway, in the guide they said use Sanden SP-20 oil for SD508 compressors, although I only found SP10, this is all I could find locally, so yeah.

Problem is I don't know how much oil or refrigerant to put in this system.
In Diavia installation instructions, they said the system takes 900 grams of R12. And in Sanden's retrofit guide they said because the system is not designed for it, I should use 5% less gas, right?
But then I changed the condenser to a Parallel Flow type! How does that change the equation? It's a totally different design and the new one is much bigger, so, what do I do?
And how much oil do I put in?

TL;DR: I can't decide how to connect the new pressure switch, and I don't know how much oil and gas to put in.

[hozzziii]

Alright well thankfully I have some smarter than me friends.
So I asked one friend to take a look at the situation, explained the dilemma.
He looked at it and suggested why don't I use a relay. Use one circuit to control the other one.

So he came up with an initial design, then I suggested why don't we go to the car, turn the key on, see which ends have power, then turn the ac switch on, see what changes.
So we did that, we found out that, the blue wire at #27 connector has switched power, as in, the ignition in on gives it power. And we also found out that the Green-Yellow wire has power after I turn on the AC switch.

So, he proposed, we take power from the Green-Yellow wire, into the pressure switch, if the pressure switch thinks the system is ok, it closes.
Which then we use to send power to both the new relay and the white wire that goes to the compressor.

I'm not really familiar with the terminology on relays, so I'm just going to explain the way I can.
We use the power that comes off the pressure switch. We split that wire into 2, one wire goes to the "control circuit" of the relay and after that goes to ground.
After which, the "power circuit" of the relay kicks in, this part we have attached the blue and the brown wire on the ends of it.
So when this part kicks in, that circuit is closed, and then power goes to the fan.
So this way, from the one pressure switch, both circuits close together but they're not directly connected, just to avoid any undesirable shorts.
This is pretty much what I got, so far.