I have a 1996 Ford Windstar and have a couple of questions?

R134

You didn't give the conditions that the A/C changes under. If you are stopped it could be that the fans are not working or a bad viscus drive if you have that or low on freon. If your on highway it could be freezing up because of to much freon.

It is possible that there are two ports that are the same size and they are on the same pressure line but there should be two different size ports on your system.

The high pressure line is the one that comes out of the compressor to the condenser in front of the radiator. It can also be identified by the size of the lines the big one is the low side, small one high side.

If you get a recharge kit get one with a pressure gauge on it, do not open the can before you check the low side pressure. No more then 45 lbs at 1000 RPM's. To much it not better, like I said it will freeze up and could ruin your compresser.

The high side usually gets hot and the low side gets cold during ac operation. You cannot put R12 in an R134a system because the fittings are different. Whatever you recharged yours with is the right stuff. If the refrigerant can didn't explode, you had it on the low side. When in doubt, check the repair manual. The public library has many from different publishers. Save yourself $30.