I am working on my 1999 LS400 AC system and there is a branch circuit that bypasses the TXV and leads to an extra port on the evaporator. I can't figure out what the function of this line is and I don't see anything similar on any other models. I originally thought that it may be an IHX for improved efficiency but based on the flow path it doesn't look like it.

There is a small "tee" off the liquid line (before the TXV) that feeds some sort of expansion device (this is separate form the TXV, see photo below).
2022-12-02 08_42_01-88503-50170 Toyota OEM Genuine REGULATOR SUB-ASSY, PRESSURE _ eBay — Mozilla.jpg

After going through the expansion device the line goes to a third port on the evaporator. The evaporator has three ports - one for the feed from the TXV, one for the suction back to the compressor, and one from this unknown expansion device. Here is a picture of the evaporator core.
2022-12-02 08_44_33-A_C Evaporator Denso 3BZP19 for Lexus LS400 1994 1995 1996 1997 1998 1999 20.jpg

When I blow into the third port it seems to be directly connected to the evaporator outlet. Its almost as if its a bypass around the TXV and heat exchanger, perhaps an high pressure relief to the suction side? The hole in the "tee" leading to the expansion device is small, almost a pinhole, probably .035" in diameter, so there's not a lot of flow here.

I have a spare evaporator I can cut open if need be, I just cant figure out what purpose this extra line serves. Any ideas?