* The specific AC system design: Different models of the 1999 GMC Jimmy might have slightly different capacities.
* Leaks: If there are leaks in the system, more refrigerant will be needed, and it won't stay cold for long. A proper leak check is crucial *before* adding any refrigerant.
* Refrigerant type: Your Jimmy uses R-134a refrigerant. Using the wrong type can damage the system.
* Compressor condition: A failing compressor might not be able to properly circulate the refrigerant, even with a full charge.
Do not attempt to add refrigerant yourself without proper equipment and training. Adding refrigerant incorrectly can damage the compressor, condenser, or other AC components, leading to costly repairs. A qualified technician should perform a complete AC system diagnosis and recharge. They will use specialized equipment to evacuate the old refrigerant, check for leaks, and add the correct amount of new refrigerant and oil. They can also determine if there are more serious problems with the system beyond a low refrigerant charge.
Instead of focusing on the number of bottles, focus on finding a qualified mechanic to properly service your AC system. They will have the equipment to measure the system's charge accurately and ensure it's working correctly.
