How to add Freon

@tammiboone to check the way the dealer does it, use the HEATER & AIR CONDITIONING SYSTEM chapter form the service manual. Page 34 shows you that.

Now, if you are like me (frugal), you get a couple of cans of R-134a refrigerant from your favorite supplier. Then park your car where you get lots of fresh air, since you will eventually have to keep it running. Next locate the Low-Pressure Port. On your Maxima it should be on the passenger side of the engine bay. It might even still have a black or blue plastic cap labeled with an "L" on it.

Start the engine and turn your AC to the max or coldest setting with the fan on high. Make sure the AC compressor clutch is actually engaging. You should hear a loud "click" when you turn the AC on Once that's running, remove the "L" cap from the low-pressure port and connect your recharge hose (make sure you get a can that has the hose with it) onto it. Next, check the gauge to see where your levels are. Usually it should be somewhere between 25-45 psi.

If you find that the pressure is low, start by shaking the can thoroughly and make sure to hold it in an upright position. You’ll want to squeeze the trigger in short 5–10 second bursts, while occasionally shaking the can and rotating it between the "12 o'clock" and "3 o'clock" positions. It's important to stop frequently and check the gauge as you go, because you do not want to overcharge your system. Also, the can of freon can get pretty cold in your hand. Use a glove if you want to.

Once the gauge reaches the "Green" or "Filled" zone, disconnect the hose and replace the plastic cap. Let the AC run for a few minutes to make sure you can feel that the temperature inside your Maxima is dropping. AS always, use common sense. You will have to do that on a running engine, so stay away from any rotating parts and do not wear loose fitting close that can get into and belts etc. It is really not complicated or even dangerous, for as long as you use common sense.

Here is a picture

that shows you were the Low pressure A/C service valve is located. This one already has a can of refrigerant attach to it :-)