If you are talking about A/C low pressure side fitting it is located on the passenger side of the car underneath the hood, you will have to look in the back it is a deeper inside.
Follow lines from compressor-Larger line is low pressure--port may be at or around the accumulator/drier by passenger firewall
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.
Low side service port is against the firewall just underneath the alternator. It has a Blue cap on it.
the low pressure port is on passegers side, between firewall and engine. the cap has an "L" on it.
passengers side about a foot down between firewall and engine!! it has an "L" on the cap.
In 2002 the Chevy Malibu had a large port 3100 engine producing around 180hp. This engine was used from 2000 to 2003 in this form.
it is located about half way down in back of engine on passengers side,between engine and firewall.
on passengers side about 1 to2 feet down at firewall, below alternator. this is the low pressure port to recharge a/c.
look for the port with the black cap on it, it's the low pressure port.
The AC low side service port on a 1999 Chevy Astro van is located next to the firewall. It is the port that is closest to the evaporator.
That would be the low pressure service port and it should be located on the receiver/dryer.
The 2003 Chevrolet Malibu OBD 2 port is on lower edge of dash left of steering column