A/C not cooling

Overcharge and undercharge both act very similar depending on how close they are to the correct numbers. The only way to see what is going on is to run the pressures and then diagnose what those and the symptoms are telling you is wrong.

STEVE W. Is one of our best! Please let us know what you find. We are interested to see what it is.

It sounds like it has a pressure leak then. The pressures are showing no charge again and it had to go someplace. I would add some dye and then start looking. I've seen evaporators leak under pressure but not under vacuum, same with o-rings and seals. I've used both plain air and nitrogen to avoid using refrigerant and just using the pressure of those to push the dye around, then hunt for the dye stain.

Yep, pretty common in A/C and other systems as well. The way the seals work they can be drawn tighter under vacuum while they still leak under pressure. Or some odd ones like a very corroded condenser core on a Ford a while back, it would leak like a screen door under pressure, but under a vacuum the corrosion would draw into the pitting and flakes and seal.
Similar issue with the o-rings, They get squished into an oval with flat sides, under pressure the sides will act like one way valves and let pressure out, then when you apply a vacuum they will draw into the split line between parts and seal up. Can be frustrating at times. That is why I generally test under both as a vacuum can give you a false result.

Yes, but you can usually get kits that include all of the needed ones for a particular vehicle. This is a picture of the kit they sell for your Nissan, lot's of places that can leak. Plus the compressor and other hard parts. It's why I would start with the dye first and then go hunting. Another trick to finding the leak, use compressed air or similar to pressurize the system, then mix up some dish soap and water and spray it all over the parts and look for the bubbles.

Those pressures are high so it likely won't work great, but you should be able to find the leak. A place to look for the interior pieces is the A/C drain under the car around the firewall, any moisture or oil can get there and drip, and you would see it on the rubber duck bill or drain tube. Sometimes it can make you want to burn the car trying to dig out the leak, some of my worst ones were tucked in the dash or a crack on the bottom of one of the lines and you couldn't see it because the dye would come out and drip off. Found it when I stuck some clean cardboard under it overnight. Be sure to cycle the A/C on and off as well, that will let things relax and possibly show up better. Have had many valves leak, a balloon or even just putting some soap in there will show those.
One of my secret weapons is the cheap bubble solution the dollar stores sell. That stuff really bubbles up with even a tiny leak and it's ready to go in the bottle.

Okay, those pressures are better. Some leaks can be a nightmare to find, especially when you are looking for something the size of a sewing needle. I have faith that you will find it, It may take a bit but any system that drops to the pressures that one was when you started is leaking somewhere.

If the pressure is coming out it won't hurt anything and will only wash the dye away. Then when you get it repaired and pull a vacuum it will remove anything from the system anyway.