checking your refrigerant level is fairly easy, all you need is a specific gauge you can get at kragen/auto zone or even walmart. in a lot of cases if you buy a can of high end refrigerant for your a/c, some cans will come with a gauge. this gauge is also required to fill your system with refrigerant when your level is low. the gauge is 100% reusable for future system refills.
here's the gauge i have, along with probably a lot of other cvn'ers. this particular one came with a can of A/C refrigerant i bought at wally world for $29.99
locate the device circled in red. it's to the passenger's side of the engine bay... the gold port is where you plug in the gauge to test your A/C charge.
turn your car on (crank the engine) and turn your A/C all the way to max and coldest. than inspect to see if the A/C clutch is engaging in at all. if it is not at all, you probably have no charge in your A/C system. (either that or your clutch has an issue) if it kicks on and off intermittently, than your system may need more refrigerant than what it currently has in it. if it's on continuously without stopping and your A/C is blowing warm, it could be the old depleted refrigerant that no longer has any charge left. because as long as your A/C system has a charge (old or new refrigerant) the clutch will engage. either that or there is more than likely another issue somewhere in the A/C system. here's a picture of the A/C clutch. its behind the radiator on the main engine belt below the alternator.
after inspecting your A/C clutch with the A/C system up all the way, plug your gauge into the gold port on the device mentioned earlier. keep your A/C on and up all the way while you do this!
see what your charge is. if you have a "charge" in your system, (gauge says it's at the correct PSI) but your air doesn't blow cold, you may need to have some old depleted refrigerant extracted out of your system before you inject new refrigerant.
here's my system charge. up as high as i can safely go, and air blows nice and cold!