Where is the low pressure port for ac recharge for a 2004 Volvo S40?

The low pressure port is on the back left side of the engine compartment. There will be a black pipe sticking up with a cap that says "9 nM Max." Unscrew the cap and you will see the port. The 9nM Max is referring to the max torque that can be used on the cap, and is basically equivalent to finger tightening without force.