[deliriousga]

Check it before adding anything. If you overcharge it, you can damage the system. Like Jim said, you need to take the course and get the certification. If you don't evacuate any refridgerant, you're not required to have a vacuum so you can check and fill. The certification is only about $25 and it took less than an hour to complete. If it is low, fill it then take it somewhere to find the leak.

I'm taking one of my cars to a local shop to evacuate the system then I will go through and replace all of the o-rings and refill it. It's not difficult, just time consuming.

Btw, if you take it to a shop and they tell you they are not allowed to top it off because they are required to fix the problem first, report them. It's a lie shops use to make extra $$ and it's a violation of their certification.