* Specific model of Suburban: Even within the 1999 model year, there were different Suburban trims (1500, 2500) which may have slightly different AC systems.
* Size of the AC compressor: Larger compressors generally require more refrigerant.
* Condition of the system: Leaks in the system will obviously reduce the necessary charge. If there are leaks, simply adding refrigerant won't fix the problem – you need to repair the leak first.
You MUST consult your vehicle's owner's manual or a reputable repair shop. The owner's manual might have a general range, but it's best to get the exact amount from a professional. They can properly diagnose your system, repair any leaks, and add the correct amount of refrigerant (R-134a in most likely in a 1999 vehicle). Improperly charging your AC system can damage the compressor and other components.
