91 Aerostar A/C recharge?

Your car is most likely an R-12 system unless it has been retrofitted. With both systems, the service ports are two different sizes. On R-12 the large port is the low pressure side. Its the opposite for R-134. R-12 service ports are threaded on the outside of the fitting. R-134 service ports are not threaded on the outside and have a single groove at the base. Do NOT mix the two! It will destroy the system. Unless you have a stash on hand, buying R-12 will be a real challenge and expect to pay dearly for it. Most of the time its cheaper to retrofit and charge with R-134 than it is to charge R-12.

Don't bother. I don't mean to be rude but if you 'add' a can of refrigerant you can actually overcharge the system. Having too much pressure is just as bad as having not enough. Take it into a shop for a proper fill. If there is a leak.

It's less cost in the long run to get the system professionally checked and refilled than it is to keep overcharging the system.

I can't say which port is the correct one, as I don't know on the Aerostar van, but again, I highly recommend spending the extra $50, and take it into a shop if you really want A/C.

That's one reason for not doing it yourself, if you don't know how.

Too much refrigerant is just as bad, if not worse than too little refrigerant. You also have to replace the oil that came out with the freon when it leaked. It's a closed system and it leaked.

If you are using r134a refrigerant the smaller fitting is low side. If it is r12 then small fitting is high side. The fittings are entirely diffrent so you can't mix them up.

Wrong!!! The low side is the larger diameter line.

they are different sizes. the low side is the smaller one