As most appliance technicians know the factory does not install access ports onto refrigerators to be sold to the public. They are tested, pressurized, and sealed off to prevent refrigerant tampering or accidental venting of the refrigerant inside. Refrigerators used to use a toxic refrigerant known as R-12 which was a highly chlorinated refrigerant much like ammonia. Todays refrigerators at the time of writing this are primarily R-134a which is a much safer and environmentally friendly none the less extreme caution must be taken when dealing with any type of refrigerant to prevent accidental atmospheric venting.
Accessing refrigerators is done professionally with two methods, the first is with a supco bullet piercing valve BPV-31
These are not to be left on a system indefinitely because they will eventually leak allowing refrigerant into the atmosphere. I personally only use these for diagnostic and leak detection although I have been leaning towards using access pliers.
Which brings me to my next sealed system access method
Refrigeration access pliers are a great way to access a sealed system but the problem is that once your remove the pliers the system is left open. But we can solve this problem with a refrigeration pinch off tool.
With a refrigeration pinch off tool we can seal off the copper tubing beyond the access pliers and once it is fully locked down you can remove your access pliers and seal off the end of the copper stub with some silver solder.