It is under the dash on the driver side.
look for the port with the black cap on it, it's the low pressure port.
To add refrigerant (commonly referred to as Freon) to a 2004 Chevy Trailblazer, locate the low-pressure service port, which is typically found on the larger diameter aluminum line between the compressor and the evaporator. Remove the cap from the port, then attach the refrigerant can with a hose to the port. Follow the instructions on the refrigerant can for proper filling procedures, ensuring the engine is running and the AC is set to the maximum cool setting. Always check for leaks and ensure you're using the correct type of refrigerant for your vehicle.
The air conditioning service port for a 2006 Chevy Express 3500 is located on the refrigerant lines near the engine. The low-pressure service port is typically found on the larger diameter line, while the high-pressure port is on the smaller line. To access these ports, you may need to lift the hood and look near the front of the engine bay, close to the compressor. Always consult your vehicle's service manual for specific details and safety precautions.
on the evaporator / dryer
You can add Freon to your 1999 Chevy cooling system through the low pressure port. Connect your Freon bottle to the low pressure port and release the Freon into the system.
The smallest with a green cap on it.
The 2002 Chevy Cavalier low side service port can be found on the top of the air conditioner compressor. The low side service port will be labeled as the low pressure port.
It's right above the high pressure port!! :) under the air cleaner box ,
Follow lines from compressor-Larger line is low pressure--port may be at or around the accumulator/drier by passenger firewall
use a pressure guage hooked to the scrader port on the fuel line.
The low pressure service port on your Chevrolet K 1500 air conditioning compressor will be the one closest to the front of the engine compartment. The low pressure service port should be labeled.