Does 1999 Pontiac Grand Prix AC have pressure switch to stop compressor from engaging?

Yes, a 1999 Pontiac Grand Prix's air conditioning system almost certainly has a pressure switch (or possibly multiple pressure switches) to prevent the compressor from engaging under certain conditions. These switches are safety devices that protect the system from damage by preventing the compressor from running if the refrigerant pressure is too low or too high. A low-pressure switch will prevent the compressor from running if there's a refrigerant leak, while a high-pressure switch protects against overpressure situations. While the exact number and type might vary slightly depending on the specific model and options, the presence of a pressure switch (or switches) is standard on automotive AC systems.