Your LOW side port is the standard 1/4" A/C hose connection. The High side IS the smaller one, 3/16". This is done so that someone doesn't use a can type recharge set-up with its normal, single 1/4" short hose hanging from it and hook it up to the high side, blowing the small 12 oz can out of their hand[and taking some body parts with it] <img src="/forums/images/graemlins/shiner.gif" alt="" /> <img src="/forums/images/graemlins/shiner.gif" alt="" /> <img src="/forums/images/graemlins/shiner.gif" alt="" />
To get good results out of your A/C system, you DO need to have a vacuum pulled down on the system ONCE you fix the leak[s]. This removes any moisture left in the system from whatever leak you once had. Water will freeze up in certain parts of the system, blocking freon flow if you've left enough of it in there. Also, as always, alloy parts/lines corrode from water in your A/C system and any steel parts rust. Both are bad for the A/C system.
If your Gen 2 Monty is like most Gen 2 Monteros, your leak is the evaporator inside the dash, basically behind the glovebox. Not a hard job at all to change out if that's what's leaking on yours.'
Another sneaky spot is the glass viewing port at the top of the receiver/drier. I've seen freon slowly leak from around the glass itself. You need the small section of metal line that comes with the new glass 'window' to fix this one.
Back to your system, and anyone elses. Just adding dye or some type of stop leak won't do much except for a lighter load on your wallet. Nether will cure a leak, only a new part will do that. The reason is that A/C systems run at much higher pressures than say a coolant system where people also try using "stop leak" like for a head gasket that's weeping.
The only time you have low system pressure in an A/C that's working correctly is when it's operating, and only on the Low side, usually well under 50 psi depending on R-12 or R-134. Once you shut the system off, the low side pressure climbs quickly up to ambient temps/pressure, usually close to the actual temp of the moment with R-12. So you're at 70, 80, 90 psi as your LOW before you know it.
High sides run all the way up to 450psi[R-134] as a norm in a hot climate.
Fix your car like you want, just don't expect any short cuts to take care of a leaking A/C system.
Let me know if you want more help