seems odd..... what is max psi on your gauge?
Also, turn on car, turn the AC on and then to max and coldest settings, then hook up the dial. Furthermore, what is the ambient temperature when you're doing this? The psi dial is sensitive to the ambient temperature, and most provide accurate readings for 75-85 degress I believe.
All this aside, if your gauge is constantly reading like 40+ psi, I'd say there's a block in the line somewhere causing pressure buildup, which is very bad, or your gauge is broken, or it's not hooked up properly.
^ note, if someone used that stop leak crap on the system before, a block is possible since that stuff can cake up in the lines from what i've heard and the entire system could need a flush.