Not to pile on.....but........
That is one of your capillary tubes that are responsible for proper metering of the refrigerant as it goes into the evaporator. You can't 'just fix' a cap tube. It must be replaced from one end to the other.
As stated above, the process goes like this:
• use 2 piercing valves
, one for low side and one for high side and evacuate whatever is left of any refrigerant into a proper container per federal regulations with a vacuum pump.
• do your tubing replacement
• remove the piercing valves and solder in 2
permanent Schrader valves. Again, one for the high side and one for the low side
• pressure test the system with nitrogen to be sure you have no leaks.
• purge nitrogen and re-charge the system with the proper amounts of applicable refrigerant and compressor lubricating oil per the specifications on the A/C data plate. Observe the parameters for BOTH sides of the cooling circuit.
• fire up the unit for a test.
• IF you are successful, you still have an old, repaired unit that was never meant to be repaired in this manner. How long do you expect the rest of the unit to last?
If you are not a licensed refrigeration mechanic, I doubt that you will be able to acquire a sufficient amount of refrigerant (probably R-22) to do the job. Any competent A/C tech should be able to do a job like this.....but at what cost?
I think you will find that after you add up all the expenses, you will find that a new A/C unit with a warranty will serve you better.