Retrofitting my A/C

So I have a 1990 Mazda B2200. Not sure if the A/C works. It is all there and hooked up but the guy before me never messed with it. It doesn't blow cold so I am going to convert it to to R-13 and charge it and see if that's all it need. ANYWAYS my real question is which port is the low side and which is the high side? If anyone has ever done this any tips or tricks would definitely be very appreciated! Thanks in advance!! :D

TL;DR
Low side service port on A/C for a 1990 B2200?

Also I will upload a picture tomorrow as it is too dark out right now.

Whoa !!!! Look into the cause of the non-operation first.

With engine off, put a 19mm socket on the compressor nut, try to turn it. If it doesn't turn, then the compressor is seized, and then the compressor, drier must be replaced, and the line to drier and condenser to compressor must be backwards flushed to remove particles.

Check static pressure of the refrigerant (if any). The low side port is 1/4 inch flare, standard for R-12. The high side is a little smaller, 3/16 inch flare, so an adapter would be needed.

You need to see if voltage is getting to the AC compressor magnetic clutch, and maybe could "jump" the compressor wire directly to the battery FOR JUST A FEW SECONDS, to see if it engages. If so, then you could "jump" the connections at the pressure switch at the receiver-drier. Or maybe the blower resistor is bad.

In other words, best to figure out exactly what's wrong, and easier and better to stay with R-12, which is still legal to use, and able to be purchased.

Converting to R134a refrigerant means different refrigeration oil, which means removing the R-12 oil out of the system.

So see if

Okay sounds like a good plan! I just don't understand the part of seeing whether or not voltage is getting there. Could you try explaining that paragraph again?

Thank you so much for the help!!

Never mind! I get what you're saying. And I already bought all the stuff to convert it to R-134a though, so that's happening as R-134a is a lot easier to find and cheaper.

You need to determine whether positive voltage is getting to the AC compressor or not, when the system is switched on. One failure mode is that the compressor clutch coil goes bad or the clutch gap is too large, and then the compressor clutch does not engage like it should. Of course, this assumes that the compressor is NOT locked up tighter than a drum.

If voltage is not getting that far, PM me with your E-mail address and I'll E-mail an AC wiring diagram. Because the voltage to that AC compressor can be "blocked" by a bad fan switch, push-in AC switch on the dash, blower resistor, AC relay on the evaporator case, de-icer switch on the evap case, or by the low pressure switch on the receiver drier. So you'd need a test light or (better) a voltmeter/multimeter to solate that.