Nope, just have to hook a gauge to it in order to determine pressure.
You can pick up the cheap recharge kits at the local parts store, but the reality is if the system is low, you have a leak somewhere - it's a sealed system, the refrigerant doesn't get "used up" at all (yes, I've actually heard someone try and explain it that way). Those kits will at least give you the low side pressure, and you can tell if it's totally dead or not.
You may have some air pressure built up in the system, if you use a small tool to depress the fill valve, and you don't see a white cloud coming out of it, chances are it's just air - but use caution when doing so, and only for a second; keep out of the line of fire when checking.

If you're close to my corner of Ohio, I'd be happy to give you a hand with troubleshooting...