I would concentrate on thermistors before changing the board. Samsung board failures are quite rare however you may want to check for voltage from the board to the 3 way valve as well as test the 3 way valve itself. Procedures should be in the fast track.
I'm not seeing anything about a 3-way valve in the fast track or the bigger Samsung PDFs. Are you referring to the device that switches the compressor between 2 different modes? I can't remember how to describe it, but at some point during yesterday's googling I read something about the thing in this photo, circled in red.Is that what you're talking about?
I checked the voltages of all the wire pairs for which a target voltage was given in the fast track on the "CN30" connector. They all seem reasonable given the temps that I think are in the compartments (I don't have a temp probe to precisely measure the real temps). I haven't checked resistances, I guess I'll do that next.