There is usually an oil in these systems mixed in with the refrigerant, so I don't really buy the "bubble" hypothesis.
Maybe better to not buy my fuzzy paraphrasing.
A tiny amount of water vapor in the system has a HUGE effect on the performance of the refrigeration cycle. This is because water has an enormous latent heat of vaporization (which is the same reason you should turn on your AC and let it run all summer without opening the windows if you live in a humid climate). Anyhow, a contaminated system would do this, and then perform well once it was evacuated (all air/water vapor removed) and recharged. Of course, the system *became* contaminated with humidity because there was a slow leak in it, and eventually the performance would degrade.
Aside from achieving a capacity bump, one reason we replaced the systems was agae (18 years) and that it did seem to have a slow leak in a coil. So maybe the 4th visit simply finally purged some water out of the system. Anyhow, if Bitt's system is old, I guess my take home is that simply recharging might not fix a malfunctioning loop.
Regardless, my room is nice and cool now and I haven't touched the thermostat once (I probably helped ice up the old system once by asking it for more than it could give).
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