I believe Snyders (McQuay brand) has that unit as a 00 model. That being your inside unit of course.
But I am not 100% yet as how Synder does there's. Which is could also be a 93 model. Its atleast 9 years old.
Make sure the schrader cores are tight at the valves. BUt, I have a feeling you need to have your friend isolate the system by pumping the refrigerant back into the condenser and pump the system up with 250psi of nitrogen and watch the gauge to see if you can see a drop in psi. But I would also check the coil, as most likely there is a leak there (evaporator coil in the air handler). If no leak is detected (heard, seen, or gauge dropping a good bit) within a 1 hour time frame (since you say it doesn't last but 2 days) than to recover all the refrigerant out of the condenser and do not open the valves. But than on the true high side on the unit to pump the condenser with 250 psi of nitrogen as well.
You should be able to find your leak. Could be leaking at a soldered joint somewhere in the wall. But only solution than is to run a new lineset.
Do you by chance know how much refrigerant has been added each time? are they weighing it in by a scale or just "guessing"? Do you know the pressure readings before and after they add refrigerant?
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