Hi again

Last night I put one can of R134a in my wife's S90. It definetely helped -- the air is much cooler now. I learned a lot about recharging A/C in Volvos by reading recent A/C posts on this forum. (There was a long one in 850 section last month.) I now know that overfilling the system is very dangerous. That is why I stopped after only one can. I suspect my car needs more, but I want to be sure how much before I add another can to the A/C system. I also learned that cheap freon gauges from Wal-Mart are not very precise. Somebody mentioned that the only way to get accurate readings from the A/C system is to connect a good high pressure gauge to the high side port of the A/C system. Where is the high side port in 960/S90? Is it easily accessible? Does it accept the same hose as the low side port? Which manifold gauge would you recommend? Thanks

Raphael