OK, OK, you win. In my next unit, I'll put a sight glass in the suction line right before the compressor. When and if I test the envelope, I'll know what actually got through the line. If I have more trouble with the existing unit, I'll stick one in it and revisit this issue. For now, the 30 degF superheat at the suction inlet will remain.
Mikesolar,
It seems to be an issue at high flow, high temp (>-10 degC), low superheat conditions. With r290 or r600, POE oil is the worst, then PAG, then mineral oil. The mfrs are recommending Shell clavus g68 or suniso 4gs oil in r290 systems due to their higher viscosity, where in r22 systems they recommend clavus g32 or suniso 3gs. Kind of like putting racing oil in your car if you like to rev the engine. If the oil thins out, it will start from a higher initial viscosity and won't get too thin or foam up.
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