All of the local auto parts stores including Walmart sell a do it your self AC recharge kit that has one bottle with the gauge on it. Pay attention to the color zones on the Gage. If you overcharge your system it will act as if it was empty.
If this does not work for you,there might be something else wrong that would require a diagnostic and repair. Thanks for posting a question this is Aaron from www.fixmycarfast.com We are a mobile repair service based out of Murietta.