Hyundai :: High Pressure On Low Side Of A/C Loop?

We noticed that the air conditioner in our 2000 Hyundai Accent isn't as effective as it once was and I began to investigate. My hypothesis was that the car is 10 years old and may just have over time become low on refrigerant. After checking that my car does indeed use a R-134a based system, I purchased a canister of refrigerant with a hose and gauge for connecting the canister. Following the directions on the product, I attached the gauge and operated the A/C at full blast. Initially the pressure read 45 psi which would suggest that the system was probably about where it should be given the outside ambient temperature. I continued to observer the gauge and over a few minutes the pressure rose to around 100 PSI before the compressor stopped turning (the clutch released, so the outside of the pulley turned normally, but the center of the pulley stopped.) As expected the cool air ceased and the blower at this point only moved around the warm air still in the cab.

All I have done at this point is observe the pressure on the low side of A/C system and witnessed the compressor stopping when the pressure got high. My suspicion at this point is there is a much bigger problem for me find? I know I can always take the car to a specialist, but I was really hoping for a simple and economical do it yourself solution.