2000 Other Oldsmobile Models

I have a 2000 olds intrigue with duel controls on dash for climate control for both sides, Now the wierd part is the pass side has cool air comeing out but the drivers side has so so cool air comeing out?I checked around and was told that ac should be top up, well that sounds kind of wierd to me, why would 1 side gives cold air and the other side is so so if the ac was low?Anyhow looking for a answear in to why it would do this. Now if the ac does need to be topped up I have a kit to do that I checked to make sure that it was the right stuff to installe but I dont know were to find the low side of the line from the condensor, I have a line on the fire wall that had a black screw on cap but the kit that I have states that I should have a blue?I tryed finding the lines from the compressor and condensor but these have everything buried though the frame and plastic covers. So any infor @ all to this problem would be great.1 Does it sound right that it is the freon that needs topping up?I would like to top it up anyways so I would need to know were I can fine this line to charge the ac.2If this is not the answear any ideal what would cause the half side cool and the other so so? It has a 3.5 v6