Freon is added into the low side ac port. Using the proper type Freon, and a gauge that works with that type Freon, connect the hose to the port. With the engine running allow the Freon to flow until the gauge reads in the ok range.
In the low side ac service port.
The 1999 Oldsmobile Alero does not have Freon in the A/C system. It contains R134 and not Freon which is R12. As I am sure you do not have the proper equipment to recharge the system plus the fact it is illegal to add refrigerant to a system with a leak, until the leak is repaired, take it to a professional and have the leak repaired. You have a leak or you would not need to add refrigerant.
FreonThe connection is on or close to the receiver dryer. If you add too much, the compressor will lock up or it won't cool very good. They don't sell Freon any longer. By the way, your car takes R134A refrigerant. If you add Freon, you ruin it.
Low pressure line Larger line running from compressor
R134a
To add freon to a 1998 Oldsmobile Cutlass, locate the low-pressure service port on the air conditioning system. This port is typically found on the larger diameter aluminum line between the compressor and the evaporator. Remove the cap, attach the refrigerant can's hose to the port, and follow the instructions on the can to add freon while the AC is running. Always ensure you are using the correct type of refrigerant for your vehicle, which is R-134a for this model.
None, the refrigerant is R134a not Freon which is R12.
R134a
R134a
R134a
R-134
never use it