It should be about six inches from the compressor. The large line.
The low pressure port on any A/C system will be the the line running from the compressor and going into the evaporator in the passengercompartment. The high-pressure port is in the line coming from the condenser in front of the radiator going to the compressor.
look for the port with the black cap on it, it's the low pressure port.
On a '99 suburban, the low pressure a/c port is on top, towards the back of the compressor, and pointed forward. The high pressure port is there also, just behind it and to the left, pointed straight up.
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.
That would be the large diameter line
No or low fuel pressure
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 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.
Follow lines from compressor-Larger line is low pressure--port may be at or around the accumulator/drier by passenger firewall
The 2001 Chevrolet Impala low side service port can be found on the top of the air conditioner compressor. The port will be labeled as the low pressure port.
The smallest with a green cap on it.