Go to AutoZone or Advance and buy one of those nifty cans of R134a refrigerant that has the gauge and hose built into the can. It might be more expensive than buying the basic cans, but unless you want to buy the kit with the valve, etc., it's the most convenient way to go.
DO NOT ATTEMPT if you don't know what I am talking about:
Find the suction schrader valve, with the black screw on cap. Remove the cap. Start engine, turn on A/C to MAX, both front and rear (if it has rear A/C). Let it run for a few minutes.
The end of the hose has a snap fitting on it that snaps onto the suction valve. You release it by squeezing the connector. Practice before doing.
Snap onto the suction valve (pull on it to test) and press button on the can, holding it as vertical as possible (follow instructions above all). Add until you are in the operating zone, at which time the compressor will run continuously (because you are on MAX). It might take more than one can.
Your compressor may not run (click and cycle on and off).at all until you put in a can if it's really low.
When you get good at it, buy a kit you can use with the cheap cans- It will save you money.
The bottom line is that you will need A/C service sooner or later. That is where I am at now with my 2001 T&C. It will prob get worse (needing more frequent recharging) until it doesn't even hold it for a few days. I am calling a friend to repair mine tomorrow. The Chrysler vans have a bad reputation on A/C issues.
Good luck, follow directions, and be safe. Things do get HOT around there, and if you are not a car person, do not attempt.