[TX Cruiser]

Your high and low are both on the top of the manifold plate on the compressor. Low is closest to the engine block and situated down lower than the high.

There is a reason you need freon, you have a leak and you ought to find it/them before you put a charge in the system. 134a is a nice change and believe what everyone says or not, it can blow cold, damned cold. 134 does operate at a higher pressure, and that's why you use 80% of the recommended charge for R12, that's a general rule of thumb. If you want it operating at peak performance you need to have guages.

I'd start your project by introducing compressed air or nitrogen into your system (100-150 psi) and use a spray bottle filled with soap and water to locate the leaks, they will bubble, imagine that. Most leaks can be found by the naked eye if you look for greasy grimey black build up around fittings and connections. The charge port valves are prime spots for leaks.

If you are going to do a blow and go, skipping the vacuuming, leak detection, and all the other stuff, you can get it cold, but it won't last forever.

Let me know if you have anymore questions.