Thanks Larry: I know where the low side is but i have a hex type nut on the right side of the sight glass,but it looks like it does not want to be touched. There is a valve on the compressor and another one on the drivers side of the large cond. fan. I don't know which one is the high side. I tried to connect my guages[red high side] to the valve on the compressor but the leak proof hose fitting is too big.