Ibanix,
All cars have a low pressure cutout. Since the oil is mixed with the refrigerant, when the pressure is low, it kills the power to the compressor clutch to keep it alive. Check at your compressor wire to see if you have power. I like a digital multi meter, but a test light would give you an idea. If no power there, use the DMM to check for continuity across the low pressure switch. It should be a 2 wire sensor screwed into the line somewhere or at the dryer. I'd look, but I'm actually on a road trip in the Jetta with the misses driving.
Here's a chart to check the static charge state of your car if you have gauges:
R134a chart I'd check it when the car is cool so you know that the system isn't heatsoaked. All this will tell you is if you HAVE refrigerant in the system. It won't tell you if you have the correct amount. The compressor should be energized if you have above 40psi or so. That's a ballpark guestimate.
If you do need a recharge, you can possibly get it close by charging the low side line (the fat one), but I'd recommend having it professionally repaired by an A/C specialty shop. Plenty of garages will "fix" it, but I train these people day in and day out, and the expertise level varies dramatically. If you were in my area, I could steer you to somebody.
Do yourself a favor, though. If you do decide to do this yourself, watch your high side pressures and don't overcharge it. I would prefer to see one undercharged. More is NOT better. Also, don't use anything with an oil charge or sealant. If it was a slow leak and the gas escaped over time, the factory oil charge should still be there. Modern systems have charge figures to the hundredth of a pound. Surplus oil will take place of that wonderful, cooling freon, and benefits nothing.
This is one area, like alignment, that you can get it close, but it's almost impossible to get perfect without proper equipment.