Help with AC

[tdangle]

I found one of my fittings a little loose, but nothing for sure as to the source of the leak. It did have a leak as it had lost some of it's charge, as once I added a can of 134 with uv dye, it blew cold again. Really haven't found the source of the leak yet using a black light. the UV dye is certainly messy though. I added a 2nd can and all seems to be working OK, Pressures are close (fan in front of the condenser lowered the high pressure). Air temp at center vent is only about 54 at 90 outside. Looks like I may look for some R12 once I'm sure the system is sealed up tight.

In learning about AC systems, the only thing I don't understand is the POA valve. I found a description that it limits the suction pressure so the evaporator is at the right pressure, but don't understand the calibration of it as to how it relates to the low pressure side of the system. Anybody have a solid understanding of the POA valve.