You need to find the leak that let the refrigerant OUT!

Yeah... it's not supposed to go away. AC systems work great when there's is the proper amount of regrigerant, but as the refrigerant leaks out, it won't cool as much.

How do you tell if it's low?? Look into the sight glass on the receiver dryer while the system is on and running. You should NOT see ANY bubbles passing by. If you do, you are low on refrigerant, which means you have a leak.

You might also check the fan on the condenser coil in front of the radiator. It helps dissipate the heat build up.

AC systems do not add cold. They remove heat to the condenser coil and it gets released by air passing by it. That's why your AC works great rolling down the highway at 60 MPH, but not quite as good in stop start traffic. Check that fan and check the fins of the condenser coil for blockage, dirt, bugs. It doesn't take much to gunk to reduce it's efficiency.

How do you find the leak? By recharging it and adding a flourescent dye. Then you runn it for a few days, then open the hood and shine an ultraviolet light around untill you see the bright green dye where your leak is. Once the leak is identified, (most likely an o-ring on a fitting) the system must be emptied, the leak fixed, then the system gets evacuated with a vac pump and recharged.

It's all in the downlaodable manual. Section 1A

So, you see, there is a bit more to it than just recharging it.

Hope this helps.