There is no need to ever change the refrigerant which is R134 and not Freon R12.
1994 Chevy lumina freon type
Fittings for 134 freon
Connect the Freon bottle to the low pressure port on your air conditioning compressor. Release the Freon into the compressor. The purchase of a Freon recharge kit will make the process quite simple.
Chances are your leaking freon. There may be a leak in one of the seals.
To add freon to a 1997 Chevy Lumina, locate the low-pressure service port on the air conditioning system. This port is typically found on the larger diameter aluminum line, usually near the compressor, and is usually capped with a plastic cover. Remove the cap, attach the refrigerant charging hose, and follow the instructions on the refrigerant can to add freon properly. Always check for leaks and ensure the A/C system is not overcharged.
R134A
R-12
No. You are looking at the wrong port. If you are looking down at the port you see, look past it to the left, beneath the air cleaner.
Should be a valve like a tire valve on one of the lines near compressor. Use the one with a blue color code (low pressure side)
Where do I put freon in a 2007 chevy impala
R-134 Refrigrant.
How much freon does it take for a 2000 Chevy full size truck