I am thinking of adding some R-134A coolant from a kit by Interdynamics since the temperature of the air from the system seems not as cold as previous years. I don't seem to be able to locate the low pressure port although I read some previous posts on other volvo models which indicate the Low Pressure port is kind of hiding on the lower left side of the engine as I face the engine from in front of the car. Also there is some kind of mark on the cap. Can you confirm what it is and is that the only place I will find the that mark?

 

You are about right on where it is.
It is located under the Power steering and coolant bottles. I believe it says 12NM on it.

 

Not sure where you live, but here the BAR (berau of automotive repair) mandated this year that anytime it is to be added or "recharged" it must be collected first and then recharged and must have documenation of both pressure and pre inspection followed by the post results as well. Such BS, but hate for you to get in trouble. Check your laws.