Product review (4 stars): It works if done properly, cannot cure leaks
The piercing valve unit on the side of piercing needle has a thin paper layer that works as a sealer. So we have to find a 1.5 to 2inches spot of strait copper tube with perfect round shape. This sealer cannot block imperfections so the surface of the copper tube has to be cleaned with very fine grit, or steel wood can be safe. Work slowly until you se a shiny surface. To be safe give a very thin layer of rubber cement over the paper seal. Before charging the system make sure to expel air from tubes, just opening the valve of the container for a second or so. You must first Tap the process tube on your compressor. The only tip I would give would be to tighten the screws until they are very firm to prevent leaks. Now that you have your compressor taped and working, you're ready to check and to recharge your system. Screw the hose onto the piercing valve and open it. (Follow the enclosed instructions that came with the valve.)
Notice the " 0 " Scale on the gauge, to the right is green (negative or in a vacuum) to the left is dark blue or black. Disregard the Blue graphs they are not needed here. We want to see 3-5 lbs. If you are low on Freon it will be negative.
Let the coolant flow for about 10 seconds then turn off the valve at the gauge, check you pressure. Remember we are looking for positive 3-5 lbs. You will have to do this multiple times. Increase or decrease the amount of time you have your gauge valve open to tweak the pressure into place.
After 10 -15 min check and adjust the pressure if needed. Tighten the piercing valve on the compressor and remove the charging hose. You still may have a leak in your system so every so often you might need to put a little more coolant in depending on the size of your leak. Many refrigerators last several years before another recharge is needed.