Lots of white noise and cross-posting in this thread. A retrofit is going to change things, and different systems work differently under different conditions.
It is difficult (not impossible) to really assess any system's ability to remove heat based solely on pressures. This is why systems are [properly] charged by weight. Retrofits and custom stuff (like an ALH in a Vanagon) do not apply here.
The manufacturer has already done all the math to determine the charge amount, and where it works best for heat removal and compressor function. Second guessing this is silly. I am speaking to a factory, unmodified, system. You can have a too low (or, marginally, too high) of a charge, and still get (to the operator) satisfactory heat removal. But it doesn't mean the system as a whole is working as well as it should, as it will still lose efficiency.
Think of it like this: a 6 cyl car can maintain 60 MPH with only 4 cylinders functioning. But those 4 cylinders are working harder than they normally would be, and the overall efficiency of the engine is going to be way down. Just because the operator only wants to cruise at 60 MPH steady and says "oh, the engine runs fine" does not actually mean the engine is in good health.
Once you throw in these modern systems that have all kinds of variables, and a VERY thin margin of proper charge amount, you can really screw things up quite easily.
Our shop garners lots of business from DIYrs and those stupid cans. Especially on the [Toyota] hybrids. Boy, you try and force a can in those and $$BIGNUM$$ stuff happens.
