What GVB was saying is that you need to take pressure readings on teh high and low side of the AC system. There are R134 gauges designed specifically for this and any AC shop will know what this means. He also listed the correct high and low side pressures readings.
see these links for information on how your AC works:
http://www.familycar.com/Classroom/ac1.htm
http://home.howstuffworks.com/ac.htm